Oh dear. Only a twin bed and one upper. Oh dear, this is a problem.
The kids are actually 5 and 7, but the 5 year old is the size of a 7 year old. They can barely sleep in the same room together, much less the same bed. I think one will have to go to grandma's stateroom to sleep. This will be a nightly battle of who "wins" the upper berth. To settle it, I think I'll make DH sleep up there.
Both kids usually fight over the sofabed in a hotel room. Ohhhh wait'll they find out it's a single! Now I'm wondering if they'll fight over the upper bunk or neither will want it.