Some serious lack of joined up thinking on this thread....... (Or people are just fucking arguing for the sake of it.)
What if someone goes out and doesn't 'SWIPE' out? 
What if someone hooks up?
blah blah blah..........
Lots of hyperbole and embellishment coming out from some on here (and not me!)
What if someone hooks up and takes them back to their room?
If someone hooks up with someone, and takes them back for a shag to their room (without the receptionist seeing!) there is a risk of that person not being rescued if there is a fire because they will not be on record as being there. (Are you people not reading what I said in my last post?!!!! Asking that is only proving my argument to be right. It's not proving the opposite!!!)
@jobjobjob
So, family check in and they "swipe" in, five in a four bed room. Then someone says "oh I need more nappies/wine/tights or whatever. They leave the room with one of the DC who wants a walk. So now three people on the room, the other two haven't swiped out as there is no such thing!
So, family check in and they "swipe" in, five in a four bed room. Then someone says "oh I need more nappies/wine/tights or whatever. They leave the room with one of the DC who wants a walk. So now three people on the room, the other two haven't swiped out as there is no such thing!
So fireman is searching the room can only find three of the four people and then what? Continues searching because there could be four?
This is such a pointless scenario. All it proves is that if the firemen thought there were 4 people in the room, and only 3 were there (coz 2 had gone for walkies!) that they would keep searching. Of course they would. Doesn't make it any less likely that someone NOT REGISTERED TO THE ROOM, could get left to burn to death if the hotel and the fire brigade thought only 4 people were in a room when there were 5! So your little scenario makes ZERO sense. 
And why the hell would the hotel 'swipe' 5 into a room made only for 4. Hotel should not be doing that. And most hotels WON'T. Again you don't make sense.
OP go ahead and book the room for 2 adults and 3 kids if you want to, (and pretend there are only 2 kids,) but don't try and pretend (like some of the individuals on here) that there would be no risk if there was a fire, and there were only TWO of your children recorded.
Don't pay any attention to some of the guff people are coming out with on here. Some people just like to argue, and cannot admit there would be a risk.
@savagebaggagemaster
snowagain - we only ever use one keycard anyway. Who would give keycards out to children when checking in? 
Yeah I am not buying that either. As if each child would be given a keycard each. 
As I said, the OP should not take many of these posts very seriously. However, do take the ones seriously that are warning you there is a risk to your family, if they're not all declared on the booking, and there is a serious fire in the middle of the night.....
Make the booking with one child undeclared by all means, but don't try and kid yourself that there are no risks in doing this...........
I'm out of this thread. Can't handle the crap some people are coming out with, the deliberate attempts to argue, and the terrifying denial from some.