They look like aphids to me, and I just read a discussion about this on the tree forum. Pay particular attention to the last comment.

Thank you! I'm wondering if Neem would be more harmful than helpful? I'm not clear on how strong it is on the scale of these things. I've used it on my lilies for the red lily beetles with some success but I won't use it on edibles. Any thoughts?

I'd first try a good spray of water once a day for several days in a row, and perhaps a band of something sticky on a wrap of aluminum foil on the trunk to keep the ants from climbing up and encouraging the aphids. GG48 has long and deep experience with plants, and if she says that J Maples are sensitive to agricultural chemicals, I'd avoid them. Even neem will have something added to help it stick to the leaves, and sometimes the inert ingredients can cause as much problem as the active ones. Aphids are fairly easily knocked off with water, and if you do that for several days in a row, it should take care of the problem. If it doesn't, I'd experiment by trying the neem on the end of one branch and waiting a couple of days to see if it causes harm. You don't want the entire tree defoliated.

It's a bit early for aphids. These might be Winter Moth Larvae who will enter the buds and eat away. Spinosad is the recommended treatment. Don't spray when things are in flower, but it is an organic insecticide.

Steve

The larva of a winter moth is a caterpillar. These are indeed aphids. And I'd try the spray with water first - the leaves are just beginning to unfurl and are at their most sensitive right now, regardless of using an organic treatment or not.