Just make sure the kids honor their mother with gifts, cards, and love and respect. You might get her a "Shoebox"-type funny card, or a small practical gift (something for her job or something).
This is not the type for asking her opinions about things. Be LEADING, but respectful about notifying her. "I wanted to let you know that I was going to doing thus-and-such, and me and the kids will be doing this-and-that, for which you're certainly welcome to join us if you'd like. Thanks."
