When I was a SAHM I bought and re-sold designer baby clothes. Bought from op shops (where I was going anyway, and I love op shopping) and sold on eBay. Any kind of re-selling though you really need to know what you're doing to make it profitable.
Years ago I also used to dog-sit. It'd be trickier with young children, but I used to get $15 a day ($10 a day for extended periods) having someone else's dog stay with us. For single days, we didn't usually walk them...just let them hang out with our dog in our big backyard, and play with them a bit while their owners were at work.