Most chains you have to be either 18 or 21 to check in.
It is one of the reasons that on most airlines it is strongly recommended that an unaccompanied minor not book the last flight of any route. If their flight was canceled or rerouted, the minor would not be able to get a hotel room.
This is from United's page:
We strongly recommend that teens who are not using our unaccompanied minor service be confirmed on flights early in the day. Unanticipated delays or cancellations due to air traffic congestion or unexpected weather such as fog, snow or thunderstorms may disrupt flight schedules and result in missed connections. If delays result in travel being completed the following day, United may not be able to offer overnight accommodations, since many hotels will not accept minors ages 17 or younger.
As others have suggested, it is best to check directly with the hotel. And do not take the front desk clerk's answer, ask to speak to a manager and get his/her name.
You wouldn't want one front desk person to tell you "no problem" only to have the manager come out when the kids get to the hotel and say "absolutely not."