Car trip, hotel stay: we bring sleeping bags for the kids.

Car trip, tent stay: we (adults) do rather durable cots we bought at Cabela's - they are a very good sleep and are 6'6" long and a good 2 feet off the ground. Kids do sleeping bags. The cots have a LOT bigger and wider overall footprint than a sleeping bag though: we have a tent designed for six (bagged) sleepers even though there are only four of us ever in it. In a couple years, we'll probably get a 2nd small tent for the kids. Only reason they fit now is because they aren't too long...yet.

Flight trip, hotel stay: we either bring one sleeping bag or none. We either book suites (Residence Inn, etc.) or some other roomier accommodation. For Europe, we just go with two rooms in any kind of traditional hotel. We expect, and are usually correct, that there will be no ample floor space.

Flight trip, tent stay: haven't done that one yet!! Probably would have to go all sleeping bags and leave the cots at home. I'm honestly not sure if we'll ever do this - maybe up into the Pacific Northwest someday...