To feel this is unfair

[Unintentionallycausingoffence]

MIL had a go at me this afternoon when we visited. DS has Autism he has no awareness of danger, he wanted to go in the garden but she said it’s too muddy take him to the field even though she knows he’ll run off. I made the mistake of saying he loves Christmas decorations which he does but subtle not in his face which these were so he wanted to go home when we arrived and she said well you should put them up at home (we won’t until near Christmas or he’ll expect Christmas now) he needs to get used to Christmas. She then began saying you never let us see him, our door was always open for them to visit as it was to everyone but they expect us to call them or go to them all the time even with a small baby. We do contact them all the time they never contact us. I’m reluctant to go over to theirs as previously FIL has taken DS out with out checking with DF and me first.AIBU to be upset

I'd expect to be invited rather than invite myself

It sounds like you've got enough on your plate without taking on MIL's demands and moods. I would try to let her nonsense go over my head if I were you. If she wants to see more of your DS, she can make the effort, be supportive instead of critical and treat you with respect.