DS with DH who is nearly 2 (in Jan) and DSD who is 12.
DS is going through a bit of a tantrum stage, he's not speaking yet and this can lead to frustration I think, and then he will hit sometimes. It's not good I know but I've been assured it's not uncommon and we are trying to deal with it as best we can.
Anyway, DSD seems to be on the receiving end of these sometimes however, I've noticed that it tends to be when she'll take a toy of his and mess with it, not letting him have it and sort of teasing him by holding it too high or behind her back and laughing at him trying to get to it. DS will then get cross and hit out.
I always tell DS not to hit but I have also been telling DSD not to take his things. DH thinks it's teaching him 'sharing' but I disagree.
I think in this situation DSD is doing it on purpose because she knows it gets a rise out of DS and it's actually a bit mean. She doesn't want to play with his toys, she wants to laugh at him getting annoyed that he can't get them which I don't think is kind or equals sharing either. If she was a child of a similar age wanting a turn to play then yes, but not a 12 year old taking a toddlers toys because she finds it funny.
AIBU in telling DSD off as well in this situation? She's 12, she doesn't need to be playing with toddler toys.
To add she is usually very good with DS but I've noticed this a couple of times now and it's really annoyed me that DH has only "told off" DS and not DSD too so I have been when he doesn't.