At a family party, my two younger children who are under 12 were upstairs with their cousin of the same age - cousin tells them that their older sister is only their half sister and their dad is not hers.
They come down to ask me visibly upset by this and confused that I would keep a secret from them. Mil then says "oh dear, are you going to tell them now" in earshot of the children.
Older sibling is in 20's so older but still lives at home and is close. Husband brought them up from very young so is dad in everyone's eyes.
There was no reason for cousin to even know as they are same age and wouldn't have known or needed to and definitely shouldn't have told my children. Her parents have obviously told her the details of it all.
I haven't received an apology from the parents or my mil - aibu to expect one? I am so angry about it because it's something that had nothing to do with them and was said at the wrong time. It's not that it was a big secret but I would have liked to tell the children myself and not at such an impressionable age!