Courtesy is very important to me, and so ever since we’ve been teaching words to Ruby, we’ve included “please” and “thank you”. These days, she tends to say “thank you” verbally and sign “please” with her hands (as long as she expresses it, either way is fine). We usually have to remind her, though.
Today, we were at a family restaurant along I-5. She dropped her sippy cup, and the man at the next table picked it up for her. Then, with no prompting from us, she told him “thank you” (and he understood what she said)! I almost died with pride.