When the child is too young to do it themselves (ie. make a card in nursery), then I personally wouldn't expect or want anything at all.
Once the child is old enough and makes a card / present, I personally think that's all that's required and it's no-ones job to do anything else.
I would never expect my husband to buy or do anything for mothers day, he doesn't expect me to do anything for fathers day. My MIL found it rather odd and brought me a card and chocolates last year as DH didn't do it lol
As for buying for the MIL, we do it together. Just a box of chocolates when out shopping anyway. As you can probably tell, it's not a big thing in this house.