Sandbox Kits are a great way to have a sandbox for your kids quickly, especially if your children are past the toddler stage. Sandbox kits are really the only way to get a larger sandbox. When your children are toddlers the all-in-one plastic sandboxes are a great option, but when they want to spread out a little more with their roads and towns, a larger play area will be needed. This becomes even more critical when there are several children in the sandbox at one time.
Of course you will want to choose a sandbox kit with a cover to keep out unwanted four-legged visitors and yard debris. You will also want to choose the spot for your sandbox carefully as it will be difficult to move once it's filled with sand, as most kits don't have a bottom.
Kits come in a variety of shapes and sizes and generally require some assembly. They are also constructed from a variety of materials, such as heavy duty plastic, composite material, or cedar. Composite material, for those unfamiliar with it, is often a combination of recycled plastic and waste wood fibers. It works much like wood and is easy to saw, nail and screw. The most important thing is it will withstand being exposed to the weather. There are a variety of items now being constructed from composite; from decks to lawn furniture.
The other common material used in sandbox kits is cedar. It is well known to tolerate moisture and is also easy to work with. Cedar has become more difficult to find and is one of the reasons that composite and plastic materials have been increasing in popularity.
Treated lumber is generally avoided for the construction of a sandbox and is becoming less popular as a construction material for projects such as decking where we are in direct contact with the material. The chemicals that are used to treat the wood so it will last longer, are thought to be potentially toxic. So it seems prudent not to unnecessarily expose our children to that kind of hazard when there are comparable materials available at a reasonable price.
Years ago, when I built the sandbox for my kids, I used untreated landscape ties/timbers. They were about 3" in diameter and 8' long. I simply cut them to make a 4' x 8' box that was about 12" high. It functioned quite well, but originally didn't have a cover (please don't make that mistake) and is still standing after years of service.
However, if there would have been the option to purchase a sandbox kit, that's what I would have done. There are several excellent options available, with covers, for a reasonable price, and they only require a few basic tools and a little time to assemble.