YANBU.
Whilst the kids are young (school age imo,) it's up to the dad to make sure they get something for their mother. And I would have been gutted if my DH had never got anything for me on behalf of our daughter. He always did though, but by the time she was college age, he told her it was up to her to do it now. For the first mother's day that she was doing it herself, she did manage to get me a card, and a box of Milk Tray. (After much nagging from her dad.)
But the next one (which was about 5-6 years ago, when she was around 18,) she went to stay with her boyfriend a few days before mothers day, and was due back 2 days after it. (She had been with him for 4 months, and he lived 50-60 miles away.)
Her dad said to her 'I hope you have something for your mother,' and she said she had, and for him to stop nagging her.
Upshot is I got naff-all, not even a card. At 4pm, I got a 'happy mother's day mum' text, which felt like an afterthought to be honest.
My mother died over a decade before, so I didn't have her to celebrate with, and DH's mother died a few years before her.
Everywhere I went that day, (to the shops for some milk, to the park for a walk etc,) I saw mothers and daughters. It really upset me; no card, no flowers, not even a box of maltesers..
What I found particularly upsetting and hurtful was that I discovered my daughter and her boyfriend had gone out for a meal for mother's day with his mother and father and sister and grandparents. There were a dozen pics of their 'wonderful family meal out' on facebook, that his father had put on, and one of the pics was my daughter pictured with her boyfriend's mother.
DH was at work on mother's day from 8am til 3pm too, so I found that particular one very depressing. DH was incensed and told our daughter to not get him anything for father's day, and anything she did get would be thrown in the bin. She never got him anything, but never forgot either of us again.
Ironically, a month later, my daughter's relationship with this boy ended!
I think it's cruel and mean to slag people off and call them unreasonable for being upset. Nobody has the right to tell anyone that they are silly for being upset. It may seem trivial to some, but the fact is, when you do everything for your kids all year round, and they can't be arsed to get you a 99p bunch of daffs and a card for mother's day; I think that's dreadful frankly. Especially as they would have a meltdown if you forgot them at any time.
And as someone said above (in answer to someone saying 'I would rather have a husband that cares all year round than one who just buys me a present on one day of the year,) why CAN'T it be both? It's like people bitch about Valentine's day by saying 'I don't need a day to prove how much I love my partner, or for him to prove how much he loves me!' Just because a man fusses over you on Valentine's day, doesn't mean he doesn't bother the rest of the year.
By the way, since that one awful mother's day 5 or 6 years back, my daughter has always made a big fuss of me. She lives away from home now, (40 miles away,) and came yesterday with a big bag full of little gifts for me, a big handmade card, some flowers, a balloon, and a cake she had made.