He has fun playing their big daddy, and gives them toys to play with. While two of the adult baby girls are playing, he seduces the third and fucks her, coming all over her face.
The following day, all three adult baby girls are now also wearing diapers, and while preparing them for a day of fun, he also does a diaper change on one of the girls, and plays with her pussy while the other two watch.
This continues for a few days and nights, as he takes enjoys sex with all three adult baby girls as he wishes, when he wishes, ending finally with all four of them in an adult baby and diaper orgy, with him and the three diaper girls.
I usually just add a good plastic pant. I work around a lot of young children, many of whom are still diapered themselves, and don't like to go overboard on my diaper of choice. Attends is what I use the most, after trying to play with my everyday underwear. When it's a requirement and not a choice, you go with what works.