Always hire a vehicle that is modern and has 3-point seat belts that are retractable, undamaged, and work, and provide space for the correct fitting of child restraints (seats and booster seats). In other words, seat belts which are just like those in a modern car.
It is important that you explain to the vehicle provider, when booking, that you will not accept any vehicle that has seat belts that are jammed, don’t retract, or which are frayed or look in any other way damaged: it would be wise to put this in writing. When your vehicle arrives you should check all seat belts.
Do NOT hire a vehicle that has no seat belts or only lap belts. Lap belts are wholly inadequate. Small children are extremely delicate and their bodies are not fully formed. Restrained by only a lap belt, in a serious crash a small child’s body would bend to form a U shape and then whiplash backwards and forwards. These movements can cause death, tetraplegia and critical injuries to internal organs. Coaches and minibuses with 3 point belts are widely available, so there is no excuse for using a vehicle with only lap belts. (In addition, many child seats cannot be fitted only with a lap belt.)
There is research evidence that using a three point belt and child seat reduces the risk of injury by 57% compared with using a lap belt on a child. The below two links take you to research demonstrating this: