Somehow the lock ring of the freewheel of daughter 2 bike managed to work itself loose and spilled most of the bearings along the road during her paper round. This caused the freewheel to alternate between fixed and free both ways at random.
Once I diagnosed the problem it was a decision between getting a new freewheel or putting new bearings in this one. I decided on the second one for two reasons. One, it seemed a waste to throw away an almost new freewheel. Two, according to t'internet it is a very difficult and fiddly thing to do to reassemble a freewheel.
Having looked at the set up, it seemed to me that all that was needed was a bit of patience and some grease to hold the bearings in the lower race, then put the block on top grease the upper race, drop the top bearings in and tighten the locking. And that was it really. The most difficult part was tightening the locking ring, as it isn't easy to apply torque with a pin spanner.
Bike is now working again, and will keep an eye on that locking ring to make sure it doesn't go loose again.