Give the boys paper and markers/colors and tell them to each make up their own card for Mother's Day. Tell them to trace their hands on paper and put their name and date on it. They can make a fan out of paper, or things along those lines. Let them be creative. You can even put a little snapshot of them on their project or card. Mothers will keep things the kids make for them (especially with their name and date of it). Let them fix something for her breakfast (a bowl of cold cereal, toast, or something microwavable) and let them take it in to her, while you stay out of it (except any supervision they need. Let it appear that a couple of little boys did everything on their own, and she'll love it. These type of memories are usually more precious than some store bought gift.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!