A number of places exist where you can find infant carriers and daypacks as well as clothing and other outdoor gear: sporting goods stores, discount stores, garage sales, family and friends, second-hand stores, Internet sales boards, and clubs. To cut your expenses, buy it on sale or off-season, which typically is January. If buying second-hand items, make sure they’re still usable and comfortable.
Despite having served in the Army infantry, I’m not a big fan of military surplus gear. Most parents will find it bulky and cumbersome. Such gear really is suited for the rigors of the battlefield, not a family day hike. Having said this, I know a number of parent hikers who wouldn’t go into the wilds without their Ranger pack.
You also might consider making your own gear. It’s not necessarily less expensive than what you’ll find on a store shelf, but constructing the equipment can be fun and teach your children some skills as well. A number of websites provide instructions on making everything from backpacks to hammocks. You’ll need to have a sewing machine for a number of the projects.
Read more about day hiking with children in my guidebook Hikes with Tykes.