I am in the process of attending 4 days of math training with First Steps in Mathematics. I have attended 3 days of training so far and have one day left later this month. The sessions are all about ways children learn math and why they struggle when we leave out certain steps or pieces. It is not a full scripted math curriculum, but rather a resource that develops and expands one's understanding of how children learn mathematics.
A few of the topics we discussed in the last session were teaching doubles, subitizing, how children need lots of practice in making 10, and mental math. One of the points the presenter made was that we should connect doubles to a visual when teaching them to children. Visual cues help children remember their doubles more easily, allowing them to free up that memory load for something else. This is especially helpful when using mental math.
I have attached a copy of a set of doubles signs that I put together quickly. They are not the cutest, but it was hard to find pictures that did a good job of illustrating the double.