I'm trying to find a children's 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 and was live action.
I'm extremely confident that what you are referring to is "The Big Wish", which as you mentioned was an Australian production, that was part of a TV series of Australian stories.
As well as being turned into the baby "to be someone that she will find adorable", his other wishes result in hime being turned into a girl, bully etc.
He was followed around by a being like you mentioned, granting his wishes. There is a trailer for the show here on Youtube, The Big Wish
