Since 10 x 10 is 100, an easy goodie bag would be to provide each child with 10 of 10 different items. The children could count the 10 items in the bag.
These do not have to be expensive items. Stickers are great, and you could actually provide 10 of one kind of sticker and 10 of another kind of sticker, and so on.
Other ideas are 10 marbles, 10 shells, 10 pebbles, 10 crayons, 10 pencils, 10 whistles, 10 bouncy balls, 10 stars, 10 strings, 10 pictures to color (make copies of the original, and make them small so that you can fit about 6 per sheet.)
One other suggestion: Child-friendly businesses are ALWAYS looking for ways to get their messages out to targeted audiences and would WELCOME the chance to place coupons in goodie bags.
Here are some examples....Ice cream places offer buy-one-get-one free coupons frequently. Sometimes karate schools or gyms will offer a coupon for one free session, hoping that it will be so much fun the child will register for an ongoing session. Call toy stores, book stores, restaurants, and don't forget hair salons. Most of these businesses like to give 20 percent off coupons for situations such as yours. Maybe you can get 10 businesses to give you coupons so that you can give each child 10 coupons.
Good luck! :)