My screen name makes my Catholic bias obvious.
I'm a proponent of proof-based teaching, and some of the (real) Thomas Aquinas teachings can easily be brought to a child's level, like the first-mover proof. A simplified version of Aquinas' "Summa Theologica", like this one --
http://www.newadvent.org/summa/ -- might be helpful to you in organizing your thoughts.
What questions have you been discussing together? I could probably offer some more specific suggestions once I know, but a general recommendation would be to look into a few books by Lee Strobel ("The Case for Faith", "The Case for Christ"), and Scott Hahn's "Rome Sweet Home" for simple, accessible arguments. These books are all stories of adult conversion (Strobel from Atheism, Hahn from a Protestant denomination) so the texts are heavy on simplified catechism.
All this is not meant to discount the value of family prayer.
Melessa, I'd be happy to discuss specific questions by PM, too, if you prefer.
Note: Like MoN, I have tried to respond to the OP's request for information. In no way is this post intended to be a proselytizing message or a denigration of other faith systems.
