Originally when I met my EXDSS, my EXDP used to allow him to get into bed with us, as they used to share a bed before I was with EXDP.
After about 6 months of me dropping hints of not being ok with this, and finding it odd that a 6 year old needed to be accompanied to sleep every night, EXDP then took to sleeping in DSS's bed, leaving me on my own.
I was not ok with that, however just left EXDP to it. I could hardly tell him not to get into his DS bed.
Now I have DC (with said EXDP) myself, I still don't allow them to regularly sleep in my bed. They are younger than EXDSS was when this all started, and one has additional needs. Bar illness, I would expect my DC to sleep in their own beds. Even my DC with additional needs sleeps on their own.
As far as I'm aware, EXDP still sleeps with his DS (who is now 12), while our 2 DC have their own beds at his flat. While it's up to him, I do think it's odd. I'd expect my DP (if I had one!) to be in bed with me.