S.H.
Put a little clorox in it.
Is it a full blown built in kiddie-pool or a folding pop up kiddie pool?
I've put a little clorox in mine to keep it clean. Other than that, you'll need to empty it and fill it up again to keep the water fresh and clean.
Mosquitoes can breed in even 1 teaspoon of water. Head's up.
I know that Avon's "skin so soft" bath oil is also great at repelling mosquitoes...you could add a little of it to the pool water...as it is made for the bath and to keep human skin soft. So adding a bit of it to the pool water shouldn't be harmful. And because there are oils in it, it will prevent the larvae & mosquitoes from surviving. You can get the Avon "skin so soft" from www.amazon.com
Good luck,
~Susan