Black Mamba is partially right. If it is one of those kids that is really young (like 5ish) Kingdra may not be the best choice. At that point, I'd let the kid choose a Pokémon that he likes the look of and build a deck for him around that. After all, kids that age probably aren't going to be winning Worlds anytime soon, and playing a Pokémon they like and know is more likely to get them to enjoy (and pay attention to) the game than winning the game is.
Actually, I just spent last night building a simple Empoleon/Golduck deck and a simple Bastiodon/Rampardos/Lucario deck for my lil cousins, because the lil gal likes Piplup (and Water pokes) and the young lad likes "tough pokemon" like Bastiodon. :biggrin::thumb:
After all, learning the game and having fun is more important than winning, early on.