Me and DH have joint account for bills, savings, other essentials and then have some spending money every month separately. I work part time as I care for our DC (toddler and primary) but we both take the same spending money every month.
I usually work Tuesdays so my youngest was in nursery but had a day off and went shopping with my Mum, something we sometimes do together when the sales are on!
I bought a few things for DC, mainly clothes as especially the youngest they grow out of them so quickly and they needed a bit of an overhaul and a few other bits I thought they'd like, nothing out there or really expensive just some little treats, new PJs and a game/toy.
My DH has 3 DC from a previous relationship, my SC. I get on well with them, in a more friend type way. They are 10 (twins) and 12.
My husband is annoyed, or more upset, that I didn't bring anything home for my SC from my shopping trip. They are staying tonight but I just took all the stuff I'd bought upstairs into the bedroom anyway to sort out tomorrow so they haven't seen it.
In my mind I'm just a mum who went out and bought her kids some stuff they needed?!
His eldest has been wanting to spend a lot more time at his mum's recently because she lives closer to his friends and I know he's worried about that. But it seems to be manifesting in some obsession with everything seeming equal all of the time.
YABU - you should have bought things for SC too.
YANBU - it's fine to spend your own money on clothes and a few treats for your DC 
It's causing friction with us at the moment this situation and I'm sick of him taking it out on me and always picking at what I do or do not do enough of.