We're working on it! We've been showing him for the past few weeks, and he has started to practice with his own arm. It's pretty adorable. He doesn't quite understand when to wave yet, but he's definitely trying to wave at people! A.Dor.Able.
That's awesome that she is signing milk...I so wish I had done more with sign language...I know it's not too late, it's just one of those "we had planned to do that..>" kind of parenting things for our family, I guess!