Superb backpack deal right now!
I know that your kids likely just got out of school. But if you are planning ahead, check out these Wry Baby kids backpacks, sold by GearXS via eBay. They could be perfect for the smallest members of your family. They are only $5.99 right now and they ship for free. These canvas backpacks come in four different styles and have a side pouch for water bottles and also have adjustable padded straps.