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Maybe Rockula?
Rockula (1990) - IMDb

It definitely happens in Bedknobs and Broomsticks when Angela Landsberry casts a spell on them; but I think it also happens in High Spirits, where it is because of ghosts (High Spirits (1988) - IMDb).

Maybe the Green Mile? With Tom Hanks?

Sounds definitely like Brother Bear but it's not an anime film, just an animated film. Other one that popped into my head was Ranma 1/2 where if a boy gets splashed with water he turns into a girl...

Try Subspecies Subspecies (1991) - IMDb

Thanks for all of the suggestions. I finally saw Bugsy Malone and thought it was very entertaining, it wasn't the movie I was thinking of. The movie I remember with all child actors playing adult...

Thanks, that sounds like it might be it. I found it on Netflix so I will watch it and see if it is.

Lately I have been updating my Amazon wish list with movies from my past and there are a few I can think about but have no clue what they are called.

The first is an animated cartoon that might...

Sounds like Pufnstuf? The boy pretends to be one of the witches for some reason and he's British. One of the witches is Mama Cass?