Honestly this crap that sm's are supposed to fill in all the parenting gaps (physical, financial & emotional) just because they have the nerve to get with a man who has kids just infuriates me beyond belief
Yes. I hate this shit.
I have no issue looking after my step children the odd time when I am consulted and asked prior or in an emergency.
I certainly would not get with a man with children and then expect to be an unpaid nanny for the entirety of the school holidays, unable to make any plans of my own or to cancel them because their mother has decided with no prior discussion that I'm having them for another week. My answer would be no and I would carry on with my plans and leave my husband and his ex to sort out whatever they wanted.
It makes my blood boil the double standards on here. You should never get too involved as a step parent, never step on mum's toes, never think of yourself as a parent, plans and contact have nothing to do with you, stay out of it until it's inconvenient for the parents of course and then it's all 'what did you expect?', they are your kids too, cough up all your time and money when mum or dad clicks their fingers because you're a family. No.
I help out, I am kind and caring toward my step children but I am not taking on parental responsibility of them, they have two parents. The same two parents they had before I was around and the same two they'd have if my and DH ever split up. If I'm at home and not busy then fine, but if I have plans... Well that's just tough really.
You've arranged childcare for your children OP, your husband will have to do the same. He is a big boy I'm sure he can figure it out, but unfortunately due to prior arrangements, you aren't free for those days.