If you still have the sticker showing the number of people that the unit can sleep, there should be seat belts for that many people. At least that's true for Winnebago 1996 model years and up (I had a 1996, so I know they posted the info that far back at least).
Clay (WA5NMR), Lee,(Wife) Codi, Brandi (Shelties) and Damncat (damn cat)
Full Timing in a 2004 Winnebago Sightseer 35N, Workhorse chassis, Honda Accord toad
We have lap belts (no shoulder restraints) in our Chinook at the sofa and on the dinnette seats. I had called our Missouri state police and asked what the rules were. They said seat belts were not required in a Motor HOme only driver and passenger seats required them. Sure surprised me. I was trying to figure how to add the shoulder restraints. My grandkids are 4 and 5 so I guess the seats they use in the car will adapt with the lap belts. Smaller kids have a 4 point restraint system within the carseats, you just have to anchor the carseats. The patrol officer said, you just don't want kids flying around within the unit.
You can use this car seat's integrated 5 point harness for kids up to 65 pounds with just a lap belt.
http://www.toysrus.com/product/index.jsp?productId=2452313
Once they outgrow it, there's no point in using a booster seat with just a lap belt since the booster just positions the shoulder belt.
Just remember that your kids don't wear belts on school buses and school buses are one of the safest vehicles on the road. There are VERY few fatalities on school buses. The law of physics says a school bus will win (by a big margin) in an accident with 90% of the vehicles on the road.