BenTennyson said:
These kind of behavioural changes will disturb your kids in a way that they might lose confidence in your position as parent, even if it might not show at first.
I agree with BenTennyson on this particular statement, however my approach might be a little more liberal.
It is important to consider that your behaviors will affect your standing as a parent, and the development of your child. The child does need to be able to look at her parents and see what it means to grow up, and she also needs to know that you and your wife are adults, and deserve the respect an attention of adults. She needs to know that you are in a place of authority and wisdom, which will be more difficult if she sees you as a baby.
She also needs to know though, that you are real people, and you have real desires, and that desires are not a bad thing to have.
The strange situation that you have here, is that in some households, it is acceptable for a parent to openly wander the house in their underwear. Also, for your situation, I'm assuming that wearing diapers and playing baby is not a sexual thing, at least when you are wandering the house fully babied. Since it isn't a sexual thing, I can see how this would compare to a person wandering the house, or sitting on the couch in their underwear, since both are just types of an undergarment.
I think you need to first consider what your goals are for your child.
1. She needs to know that you are a father first, then a friend. Parents have the important role in a child's life, of making sure a child does things, that the child might not want to do, such as go to school, learn to use the toilet, or not to touch the stove top.
2. She needs to learn to use the toilet. Maybe not as fast as parents often push their children, but she should be prepared to use the toilet when she starts going to school, otherwise you risk her experiencing a lot of bullying. I am a believer that potty training can be pushed too hard on children, but I still think it is important in their development to learn, even if I think that wearing diapers is better than using a toilet. Since seeing you wear diapers would make it more difficult for her to want to learn to use the toilet, you should probably restrict her knowledge of your diaper wearing, at the least until she has learned to use the toilet.
3. She shouldn't be exposed to any of your sexual behaviors. Early exposure to sexuality is a major problem when it comes to child development. Any amount of your diaper wearing that is sexual, shouldn't be exposed. You don't have to act ashamed about it, and it is probably good to teach your child not to be ashamed of sexual kinks, but that is something to save for the birds and the bees talk, and I wouldn't be too specific on your own sexual kinks, but just that you have them.
4. She needs to be safe in her schooling. A young child is prone to blabing at school, if she knows you wear diapers, and then talks about how you are a baby at school, she is prone to bullying over having a parent that is different than others. Be sure that her amount of knowledge about your little side, is not more then what she is safe with in concealing.
5. etc, whatever other goals you find important.
If your wearing diapers and being a baby compromises any of these goals, it would be in your best interest to change your habits until the time it is appropriate.
My opinion on how this will all affect you is this. I don't see why you should hide your diaper stash anymore than storing it in your closet or drawers. If she finds them, it is because she was exploring into your privacy, not because you were putting it in her face, you can be respectful of publicity within your house without being ashamed of yourself.
You will probably not be wearing exposed diapers around her, especially when she is potty training. Maybe you having to use the potty will be an inspiration for her to learn how to use it. I wouldn't say that you have to isolate her from knowing you wear, but probably isolate from knowing why. Remember, wearing diapers doesn't mean a person is a baby (even though in your case it does), it just means they are incontinent (which for you it actually doesn't) which is perfectly normal, but you should still encourage her to learn to live as an adult. Edit: Also, I wouldn't see the harm in wearing diapers while pants or shorts cover them up, if she notices, it is because you are wearing them as normal underwear, as a normal adult.
I can imagine that there is nothing wrong with you showing off your little side by wearing footed pj's around the house, or having stuffed animals with you. There is nothing wrong with that, and it is perfectly adult to have those things. However, manifesting behaviors such as babbling, and loss of fine motor skills, will give the wrong impression to your child of your role as an adult, and also the wrong impression of how to interact with the world when growing up and becoming a functioning human being.
I honestly can't tell you how to determine when you should and shouldn't be fully exposing a diaper, because in some societies, a loin cloth is an appropriate attire, and as I said before, in some households, open exposure of underwear is also appropriate within the family. I would say though, that during potty training, it is extremely important not to.
You are going to have to decide what type of environment you want your child to grow up in, and then create that environment, regardless of how much it alters your current lifestyle. It will be a balance between making sure she understands what it means to be a normal adult/how to grow up, and on the other hand, knowing that she does not have to be ashamed for being different, just as you are not ashamed.
Best of luck, at least you have a little while to figure it out, but it certainly is going to start fast. As BenTennyson suggested, a lot of it is going to have to move to the privacy of your own room, and at times when your child is either asleep, or not around.