If you start to disrespect the character you're playing or play it too much for laughs that can work for a sketch it will sell some gags but it's all technique. It's like watching a juggler - you can be impressed by it but it's not going to touch you in any way.
The single most important thing in a child's performance is the quality of the teacher. Making sure a child spends the maximum amount of time with inspirational teachers is the most important thing.
