My kids sleep with me, so I don't think you should feel pressure to move him to a bed because that's what other kids sleep in. We all just do what works for our family.

I like LS idea, and I would explain that he can get out, but it's important to try and stay in bed until morning (if that's what you want). Some people use a little light or alarm showing 7am so the child knows when it is morning time.

I think it could be beneficial for him to learn some responsibility and show he can stay in bed himself, but obviously only when you're all ready.