2 rocks and old jeeps

two rocks...
...old jeeps.
I've been thinking about 2 rocks and old jeeps a lot lately. You see, two rocks and old jeeps have been the boundaries that Chris and Nate have had since they started to play out front. They have always been really good about staying between these two landmarks which can be found 3 houses down to the North and South of us.
But 2 rocks and old jeeps won't work forever. The boundaries must grow and will grow with them. When will it be o.k. for them to cross the street on their own? Walk to school? Go around the block by themselves? Ride their bikes to the park? All of these thoughts make me appreciate these simple boundaries while I can.
Setting them free and trusting is tough.
Knowing that they're somewhere between 2 rocks and old jeeps is something that I savor, because someday I will have to release them to the other side.