Such great suggestions here - SR really is a great resource for so many things. I second (& third, etc.) what so many said here.
We LOVED our sandbox growing up - spent hours there summer after summer. We would build these elaborate race tracks for my brothers' matchbox cars and play with them until our play or the weather destroyed them. I have some great memories in the sandbox my dad built for us.
Why shouldn't your kids have those great memories in a sandbox mom built?
The kids workshops that Ms. Pink mentioned are awesome! Home Depot has them in our area the first Saturday of the month in the morning. My brother has a gaggle of kids so this is great for us - it's free and the kids get to build something. Check it out!