My wife is a nursery nurse and I used to do a few nurseries regularly for council.....the council has now bought a council carpet cleaning machine and "trained" the caretakers how to use it.
Wife's nursery has had them done twice now, both times over a w/e, and both times she said the place stank when they went back to work on the Monday......carpets still very damp.
Think they leave more contaminants in than they take out but they get a tick in a box and it's cheaper.