Partner has two children (6 and 8) from previous relationship. We moved in together around 6 months ago. Children stay with us Wednesday and Saturday.
On Saturday afternoon, we all go to the same leisure center. I go to the gym while partner and children attend sports clubs. Partner finishes half an hour later than the kid's session, so I collect them and we do a Saturday night "treat" shop while we wait for their dad to finish (go to pizza counter and let them choose toppings, pick some snacks for watching a film later).
This week, while we were in the supermarket I asked if they'd got anything for their mum for mother's day and they said no and seemed a bit down about it. I asked them if they wanted to choose something for her while we were in the supermarket and they seemed really excited about this. I ended up maybe going a bit overboard: got one of the hamper baskets and then got chocolate, face masks, baths salts, bubble baths, slippers socks, chocolates and a little potted plant to fill it and a big card.
We sat down and put it together when we got home and they wrote the card and were very excited. When partner saw, he raised his eyebrows a bit but didn't say much.
Children were very excited on Sunday morning to go back to their mum's and give her their hamper.
Found out today that she's made a comment to partner about not knowing why I'd have done that and seemed to imply it's not my place. My mum thinks I overstepped too.
I honestly just wanted to help the children do a nice thing when they're obviously too young to do it themselves.
Was I being unreasonable to get involved with mother's day? Should I apologise to her or just forget it and move on?