I find with little kids that texture really appeals to them. I try to use flannel whenever possible, at least for the back if not the top as well. And they LOVE the feel of satin, so I try to incorporate a narrow satin border somewhere, or put some satin into the blocks.
Most kids are pretty open to any colour scheme, but personally I don't like really loud, bright schemes which is what you often find in kid prints....for that matter I find most "kid prints" pretty awful. I would rather the print(s) did not carry the design.
My sister and I like to make baby quilts for charity, and for that purpose stick to simple designs when possible. We have a Pinterest board called "Baby Quilt Awesomeness" you may want to check out!