There's quite a few, some more regular others on and off, sadly covid caused a few to stop.
Last weekend was "little big land" in Birmingham I believe.
There is NGM down in Hampshire that is mostly a bi monthly school role play event but they also host a Preschool event too for ABDL's which is pretty good, runs about 6 times a year.
I believe there are still a couple in and around London though ABC has gone under.
One is Ageplay London Munch next on 17th May.
There have been a couple events in Bristol but the organiser stopped due to health issues and lack of support running it.
There's Strapmore School in the west midlands (another mainly school RP event).
There's a Littles/CG's munch in Wigan.
the BBB in birmingham used to have a Littles/ABDL play area, not sure if they still do as I know they stopped it for a bit a while back.
The Littles retreat in Walsall, May 12th is next one. mainly L/CG but also ABDL friendly.
Central Belt Ageplay Munch in Glasgow
Hoof it in Surrey is a 2 day (16th to 18th) camping event aimed at Pony Play fetishists however they also run the "paws Puppy" event alongside it which says "Paws Puppy Camping will be running alongside Hoof It! with a variety of goings-on catering to Puppyplayers and ABDLs" and will have a littles area.
Ageplayers Reading is around.
Teddy bears picnic in Bristol runs a few times a year again aimed at littles but ABDL friendly.
Ipswitch Ageplay Munch runs every 2nd tuesday every other month.
There are others as well, this is just the ones advertising well in advance, some don't advertise the event until close to the time others you can find from word of mouth and some you just have to find the right groups as they don't advertise quite so publicly.