They should have gotten and EXTREMLY short boy to play Bobby
Ok since this movie totally exaggerates all the Bradys' traits and characteristics, who thinks it would have been funny if Bobby had been really short, like shorter than a normal kid his age like way shorter than Cindy even.
Marcia was exaggerated by being more conceited, Jan was more psycho and squinty eyed, Cindy's LISP was overdone, etc so I think it would have been funny to make Bobby shorter.
There were several episodes where Bobby was teased about being short, esp my Cindy and Peter I remember, and one episode even dealt with his "height problem" where he tries to stretch himself.
Just because we lose today's battle doesn't mean we've lost tommorow's war.