Identification of wish gone wrong type childrens film

I'm trying to find a childrens film (possibly TV show episode), that was likely either British or Australian.

I don't remember much about the film except that the protagonist was a male child/tween who wanted to be closer to a girl. One of his wishes resulted in him becoming her baby.

There was some kind of entity following him and responsible for granting his wishes.

Film/show was likely made in the early 90s.