You can make a lot more for certain items on Ebay, they just have to be small enough to ship.
Things that sell for a lot of money on Ebay:
1. Used higher end kids clothes in good condition. As in Gymboree, Gap, and more expensive stuff but even less expensive brands will sell if its in great condition. Sell your child's entire resellable wardrobe for one size in a lot. Don't include anything with holes, tears, stains, etc. Use flat rate priority boxes to ship, its much cheaper. I have made $100 off my daughter's used clothes from one year on more than one occasion. You may get 50 cents a piece at a yard sale.
2. Used toys, examples would be littlest pet shops, legos, polly pockets, Barbie stuff, those little Peek a blocks. Wooden train sets sell for a lot. Again sell in large lots and ship in flat rate boxes. I once sold my dd's LPS collection for $150 to a lady in Poland, there were maybe 75 LPS pets and a couple small buildings. Yard sale, I would have made maybe $20?
3. Used kids books, again, in lots. For example, if you have the Magic Treehouse series books 1-28 even in so-so condition these could go for upwards of $40. Or if you have a bunch of those hardback Dr Suess books leftover and they are in good shape, they will sell for close to $2 each, again, in lots. Yard sale you might get 50 cents a book. Use media mail rate.
4. Video games (Wii, NinDS, etc) resell for a fortune
5. DVDs also resell well if not scratched