If it were me, I would try to hold out a bit longer. Typically I expect 2 weeks for transitioning but a one year old is young and may need longer to adjust. It's a big change for a little one! If I was seeing at least SOME improvement, I would tough it out a bit longer.

If you are done though and you don't think you can safely care for him and the others anymore than there is nothing wrong with telling the parents this and asking them to find another daycare.