My ex said the same. I left, had one hour to pack what I could and thought he would be reasonable. Now months on and the children have nothing besides a few books and teddies I packed. Every other toy is at the jointly owned home that he still lives in and he's told me I won't get a thing.
My advice, if I could go back and do it differently- Would be to set a date you're moving out, don't tell him, when he's at work go in and remove 50% of everything. Never go back. He may take you to small claims court but he won't get far.
Your child deserves 50% of their belongings, you deserve items that you brought into the relationship, they do not count as 50%.
My ex has now changed the locks, even though we jointly own the home. He refused mediation, refuses my offer to buy him out, won't give me an offer to buy me out, won't sell to a third party. Every step with the children, the house, the belongings is about control.
But, be warned. If you did follow my advice he will lose it and his behaviour may escalate as he has lost control.
If I could I'd hire a van tomorrow and grab my children's belongings and our memory items including all the last photos I have of my dad. Don't let him control the situation. Good luck.