Information and registration for the Sit & Knit is here.
The knitted hat we recommend for adult/children can be found on the Lion Brand website.
This hat is easy (all garter stitch) and it can be unisex and made with or without the pom-pom on top. Adjust the stitches to below 70 for a child's head, keeping the gauge in mind.
Also, if you are interested in knitting for charity and want to find groups where you can knit with others, or want to find a group that could help out folks in need, check out their Charity Connection.
It's a great place to source for groups doing good work in the world!