I absolutely love that my son is interested in the garden. I have a feeling he's more into the dirt than anything, but I'm ok with that. He's been coming into the garden with me, and I've been explaining to him that we don't rip up plants or step on them. Of course I know that plants will be destroyed, dirt will be thrown, etc - but I'm ok with that. It's part of the learning process, and for heaven's sake they're just plants. They'll grow back or they won't, and if they don't grow back I can plant another.
I was working on prepping the bed earlier this spring, and he was helping me. The best dirt work involves bulldozers, I hear.
Our garden time has paid off - when we went to visit his great-grandparent's he was very good about only walking on dirt, rocks, or planks when he was wandering through the garden with us. My grandmother was very impressed, she was sure he'd accidentally destroy at least one plant.