Double Subverted: And then his voice returns to the original one.
Parodied: Bob is regularly mistaken for being female due to his voice actress, no matter how manly he tries to act.
Zig Zagged: Sometimes Bob is voiced by a woman, other times he's voiced by a boy.
Averted: All characters are voiced by members of their own gender.
The people in charge of hiring voice actors couldn't get any decent child actors for their characters (or they do have child actors, but most of them have gone through puberty and can't do the high, kiddie voices anymore), so they got some adult men (or women) to do voices of kids.
Or, the voice actors they hired are really good at voicing both sexes, whether or not they're children.