I know some people say, "every day is important, who cares if they forget mother''s day!'... but I don't agree with that. Of cousre I love hugs and time with my family, but when they choose to forget you on a generally celebrated day, it is hurtful.
I am a confident woman, but it is nice to be remembered and shown extra appreciation one day a year... is that so much to ask?
Now, as a single mom with a family that isn't concerned about these types of holidays, all you can really do is teach your child to appreciate people. That means you encourage him to do something special on Father's Day, Grandparent's Day... set the precedent and when he hears Mother's Day is coming around, he will eventually pick it up on his own when he is older. But for now, you just have to deal with it. Spend time with your family and don't expect anything from them and try not to take it too personally.
My mom gets really uptight if we don't do enough for her on Mother's day... she doesn't realize that us spending time with her and taking her to brunch is her Mother's day gift. I know some men forget their wives who are the mother of their children, but remember to send flowers to their own mom's... so everyone is going to have a different view on this.