They will need seat belts, but the lap belts should do. It's also safer the the folk in the back (and front). I bought my lap belts from a scappy and they were fitted in a few hrs.
There is no legal requirement to fit seatbelts to side facing seats,however if they are fitted they must be worn. Children under 12years or 130cm are prohibited from being carried on side facing seats with or without a belt.
