If its eyes are open and its ears up (as opposed to plastered to its head) it is likely pretty much independent. I suggest just returning it to the spot where your son first caught sight of it. If there are bushes, trees etc. for cover, that is the place to put it.
I suppose you can offer it goat's milk, but it should also have water in a shallow dish and some grass, weeds like dandelion, clover or plantain etc. I don't recommend giving it vegetables from the garden etc. The bun may not be fully weaned, but cottontails munch on vegetation as soon as they can find it. This bunny may be tiny, but it may be older than you think it is. Even if not, they grow up very fast.
I suppose you can offer it goat's milk, but it should also have water in a shallow dish and some grass, weeds like dandelion, clover or plantain etc. I don't recommend giving it vegetables from the garden etc. The bun may not be fully weaned, but cottontails munch on vegetation as soon as they can find it. This bunny may be tiny, but it may be older than you think it is. Even if not, they grow up very fast.