Hah, yeah, we get the same sort of thing occasionally. Our 4.5 and (almost) 2yo are in a bunk bed. Sometimes my son (4) will just repeatedly come up with dumb reasons why he shouldn't be in bed. You can handle each on of these, but at some point a straight up and and firm "No. It's bed time." in my "I'm getting annoyed" voice is what works. Sometimes that means I have to stand outside their door for half an hour and keep putting them back to bed until they get the hint, but if you generally only have to do it a couple of times before they get the hint.

I only recently figured out how to phrase it, you can be "firm" without being "strict". You don't have to be a shouty monster to have limits, boundaries or firm ideas over what is acceptable behaviour. Kids seem to like consistency, they like knowing what's what, that doesn't mean you have to be horrible about it.

We're all making this stuff up as we go along, and every child and situation is different though, so you've got to go with what works for your kids.