Yes, but if they are required for safety reasons in the UK why take the risk?
Booseters are designed to stop the child from slipping under the seat belt and crashing into the back of the seat or into the person in front.
Air bags are larger volume on US vehicles because its not a requirement that you wear your seat belt in some states, so the airbag has to be bigger to take the greater forward momentum of the body.
However, would you not wear a seat belt?