Alison, I am sorry you had a meltdown, they happen. It is how we handle them that matters. Mini 2x4 very small one---staying home was not the best move, it only gives you more time to "think" don't let them / him take up anymore headspace. Are they worth making yourself miserable for,wasting a day? You have your own children and they need you. I know you don't always see that but a mum is always special,even when we are not showing it to them. Didn't you go away on holiday at Christmas one year? Try to either make it totally different or as low key as possible if brings you down. There are plenty of charities, soup kitchen that are crying out for volunteers on Christmas day, helping others is a great lift and you never know you just might have fun.
As for the baby,she is a totally innocent in all of this and who knows what her life will bring. Come on Alison, I know you can get over this. Wishing you peace in your heart this Christmas time.