When looking for a canteen or a water bottle, make sure it seals tight and can be stored upright in a carrying case. The carrying case should hook to your backpack or fanny pack belt. You don't want to place canteens or water bottles loose in your backpack, or they could drip, leaving your gear and extra clothing wet.
Another possibility - and one popular with kids - is a hydration system. The lightweight plastic bag connected to a plastic tube can be filled with water and placed inside the daypack or a fanny pack (some backpacks come with them built in). The child then can drink water as walking simply by sucking on a tube, as if an astronaut in a space capsule. Since it's so effortless to use, kids tend to stay hydrated with it. Some hydration systems will hold up to 35 ounces of water, which is little more than a quart.
Read more about day hiking with children in the guidebook Hikes with Tykes.
