Jeskai Striker is a great precon, and one of the best you can get in Jeskai colors
As far as kill cards go, you really can't go wrong with Elemental Eruption
All of these cards can be cast for their front side casting cost, or the alternate More Than Meets The Eye cost, to have it enter the battlefield converted on its back side, similar to transforming effects found on many werewolf cards
They really get back to the basics, and for kids in particular I think they are an effective way to focus not on what Trample does, what Fly does, and so forth but on the REAL way to play the game
Control players keep opponents guessing whether they have board wipes or not, but if you drop a couple of creatures and they destroy one of them then you can guess that they dont have a wipe, indicating that you should follow up with another creature
Attached to an evasive creature like Invisible Stalker, this card ensures your life total never gets close to 0