Yes, I know this well, as I said I vend and I give out freebies. But my question is kinda 2 part- what kind of items would parents like to see as freebie items for kids (that I could give out on my table with me fronting the cost) and what are some general kid friendly products for sale that folks would like to see more of in artist alley.
In my experience at huge conventions like San Diego Comic con, Phoenix Comic Fest, Salt Lake Comicon, etc. there are actually quite a few younger kiddos tagging along with their parents. With Phoenix having the most kids. I'd say 40% of my sales are to those under the age of 16.
One year I sold yo-yos with chibis of my art on them. Totally sold out! Didn't do them the next year because the company that made them for me went out of business. 
My partner in crime made a science word search to give away for free to promote our science comic. Those did okay, but I feel like the kids weren't too interested. (apparently word searches are something they do in school as homework? what?)
Come to think of it, at Tucson Comic con there was a plushie vendor that also sold baby bibs and some freaking cute hand made geeky baby items. I thought that was very creative! Nothing for free there, but a good solid products to sell.