4 years old and queen sized bed?

My husband and I currently have a queen, today we ended up ordering a king sized bed.

We’re debating what to do with our queen, our son is currently in a twin (he’s 4.) and he hits his head on the wall and ends up kicking the wall a lot and he rolls a lot.

He thinks we should store it (we really don’t even have a place to store it.) I think we should store his twin and move the queen into his room.. he loves our bed anyways.

We looked into bed rails, and found one that will fit the bed and well also be putting it into the corner.

It’s 1 FT taller then his bed right now...

We’re currently going through step parent adoption & we don’t want the home assessor to think we’re crazy. So I’m turning to y’all for opinions

We’re expecting another LO in May!

I have debated maybe storing the frame and just using the mattress and box spring but my husband thinks that looks bad too...

Thanks!