I went to a Halloween party last October at an ab/dl's house and it was close to the benchmark for good abdl events. Some people were in full baby gear(myself included. Got to show off my cute onesies) others wore more normal Halloween costumes with padding underneath or no padding if they were a Big. There were change spaces set aside and fun stuff like Lego and other toys. Alcohol was also allowed which let me slip into my little self more easily.
If I were allowed to delve into the realm of pure fantasy, I'd love to be able to rent out a space and have it made up like a full daycare with all manner of infantile paraphernalia. Playpens, cribs, changing tables, toys, a large supply of diapers, and of course caretakers that would love to take care of a room of big babies.
Realistically, I'd like more events like that to happen or for my local dungeon community to have a play space at the monthly play parties for ab/dl/littles with toys, colouring books, candy and maybe even with some furniture like high chairs or a bouncer on a suspension rig or something.