Well, I have like 2,5 ideas. ^^;
First idea is that a man who became a father just recently is complaining about his baby alot,so his wife or mom decide to show him that baby's life is not that easy ether and force hi into second childhood.
The variation of this idea is that thanks to gypsy curse or somethimng similar man's wife thinks taht he's her baby and he can't prevent anything that she do to him, though eveyone else see the truth.
My second idea is based on this brilliant series of arts -
https://diaperedanime.com/gallery/sho...e/0112/cat/514 (starting with this, there are more, if you somehoe missed the awesomness)
The guy with bed-wetting problem participates in expermental programm for curing such problems with humilation and discipline. He finds out that his girlfriend or simply the girl he secretly iked for a long time, is working there as a nurse.
Say, which would you prefer.