First up, I totally get wanting to do this.
In all the years I tried exploring my AB/Little side I never felt quite right, kinda like imposter syndrome I guess. I just always felt like an adult pretending to be a kid, like an actor taking on a role rather than actually feeling like a little kid. Once or twice I managed that real feeling and it was great but I find it so hard to get there, perhaps with the right partner it might be easier. But this is I think one of the reasons I am drawn more toward the CG roles, I can still explore and play with the little one I'm with but don't have to worry about not feeling authentic.
My problem with someone like yourself using parenting books and "mummy/parenting" groups to research how children think/act/see the world etc. is that they are all written from the perspective of an adult in a care giving role over a child not the child's view themselves.
Any parent, carer, doctor, psychologist, teacher and so on will be looking at children's behaviours and thought processes from a point of trying and help mould that child and how best to help them learn and grow into a functional adult. It's possible some of them may have some pretty deep understanding of what and how children experience things and the reasons for that but the interpretation they give will always be skewed towards a "corrective" or "supportive" or "educational" etc. Stance even when they take the "let children be children" line they still aim to nurture and support growth.
Whereas an AB needs to take the reverse of that and learn how to put aside all the growth and development they have learned or had drummed into them over years. A lot of which is simply impossible without severe mental impairment. As an example of that...
Shut your eyes for a moment and picture a beach, any kind of beach, with or without people, think of the colours, the sights, sounds, smells, seaweed lining the tide, the foam on the waves washing up and down, seagulls flying around, the texture of the sand under your feet...
Quite easy right, almost like you were there. We've pretty much all seen a beach and have memories, sensations, sounds and smells associated with it.
Ok now try to imagine being on the international space station in a completely sealed, filtered and controlled environment, there's now gravity so you are just floating there but it's not like swimming, you have nothing to propel yourself from every slight movement moves your body in unforeseen ways, the only background noise being the hum of machines, no natural sounds, no distant highway roar. Imagine tipping out a cup of water, how do you even do that when there is no gravity to pull it out of the cup, how does the water look, move or feel when you finally do get it out...
Still possible, we have seen plenty of movies/tv in space and have an idea of how it should be but with no real personal experience it's harder to actually feel and believe it.
I could sit here and describe other scenarios that would be almost impossible for you to imagine, a Hypercube for instance, we have models and theories but it is impossible for us to really know what a 4 dimensional cube would actually look like.
This is kinda similar to how children might see things, imagine a 3 year old who has never been to or seen a beach before, not even on tv. The best you can describe it to them is "it's like a sand box but much bigger, with a huge open sea beside it." and that really won't do it justice, imagine now taking that 3 year old to a beach, how breath taking the scale of it is the wonder and excitement of discovery and adventure in everything around them being an entirely new experience with nothing they have seen before preparing them for it.
You will never get back to that point where the most simple things around you are brand new but you can try to bring a little wonder into your life by exploring things in new ways or taking time to really see things.
I went on a bit there so as to the second part of your question, the difficulty there is I could write entire volumes on what I see from toddlers and young children, I work in early years so it is my job to get into children's headspace and work out how each child see's things and thinks so I could probably give quite a decent portrayal of thought processes and children's POV.
The problem with that is that children at that age are a lot more varied and individual than people realise, there are so many things that can change a child's perspective and thought patterns that there is no "one size suits all" answer. Also given my own experiences with trying to enter my own little headspace even with all the things I know and have seen, it didn't help.
Sure understanding things from a child's perspective can give you some good insights and ideas, you might learn how to "replicate" a behaviour but that might not help you feel like that child. What's more important than that is learning what it is that makes you see things like an adult and working out how to smash those foundations and break the barriers that will allow wonder and adventure back into your world.
For example I have watched children spend over an hour just dropping an object in a water tray, over and over, because they were fascinated watching the splash and ripples and how other things moved on the surface afterward, an activity that an adult would probably get bored of after 10 minutes, even someone in little headspace, because they have seen it so many times already.
The best advice I can really give is just to take time with everything you do, really look at things find the details you miss most of the time, just stop and enjoy what you are doing, seeing, hearing, smelling, touching etc. experiment and explore.
My challenge to you...
Go and get:
1 cup salt
2 cups flour
1 tablespoon vegetable oil
Slowly add water as you mix it in a bowl, using your hands no spoons/tools allowed, until you have some nice some playdough. While doing this take time to really think about how it feels on your hands, not just does it feel nice or gross but explore the texture, how does it actually feel. Look at how it sticks, why it's sticky, what changes in the dry ingredients when you add water, how much do you need, what if you add to much does more flour bring it back.
When you have a good dough really dive into that texture, press it against your skin, different parts of your body, hands, face, arms, legs, feet, tongue, ears (carefully) squeeze it, stretch it, rip it, cut it, rub it, bash it, roll it, shape it, smell it, use your elbows instead of your hands, drop some in a bowl full of water and play with it in and out of the water, how does that change it, what does it feel like now, what about adding food dye and kneading it more, does the colour spread evenly, is it streaky, why is that, what if you make two colours and mix them. Throw it in the air, throw it at a wall, put it in the fridge for a bit, stick some in your pants!
Find some toys or other objects and press them into it, try and push it through things, wrap them up in it, use poster paint to colour it (might need more flour or it gets sticky) and try making marks/drawing with the painty playdough, grab some sand or gravel or small stones/twigs/leaves/herbs/beads/wool/buttons/sequins etc. and mix them in, how does it look and feel now, can you do anything new with it. Leave it on the table for a couple hours to dry out, how has it changed, make shapes and put them in an oven (with grown up supervision) for a bit to harden now you can paint them, stack them, use them for other toys or as decorations...
Just spend time exploring and really focusing on all the aspects and sensations of what you are doing do things that adult you would think is gross or wrong or a bad idea (don't be too stupid though). Use your whole body including your tongue, allow all your senses to give you information and you will be using the mindset of a small child.
On a random side note, really young children explore a lot of things with their tongue and putting things in their mouth even after reaching an age where they know they shouldn't and understand why. There is a really good reason for this, the tongue is exceptionally good at giving the brain accurate feedback about texture and how things feel and the brain stores and recalls this information well.
For the vast majority of people If I asked you to imagine running your fingers over an orange and how it feels you might think "bumpy" but if I then told you to imagine running your tongue over the surface of the orange you brain is able to recall that texture almost as if you were actually doing it right then and there. The memory of texture on the tongue is a deeper and more physical memory than that of your skin. Sometimes even for things that have never been in your mouth like if I told you to imagine stroking a cat and then licking the cat, you can probably "feel" the fur on your tongue more than your hand.
*edited to add*
Holy crap I looked back through this after posting and I think it's the longest post I've made since my threaded armour review LMAO sorry for the essay.
good luck!
and while I do understand the thought that little space should feel better if it's more realistic I have not tried too much to do a live study of how kids realistically come to the decisions they make or feelings they have to reflect on how my own little space should be.