most likely overwatering.

what is the condition of the area they were planted in? straight into the ground? in a flower bed? raised flower bed? any compost or mulch add? shady area or full sun?

Recent transplants will not absorb water fast enough to keep up with the metabolic demands made by foliage in bright sunlight. The water is in the soil, and some of it gets up to the leaves, but not enough to prevent wilting. The solution is to shade the plant from sunlight, temporarily. The shade does not have to be 100% to be effective, just get something up during the sunniest part of the day. The roots will recover eventually, and gain the ability to absorb and transport sufficient water. This might take a week or two.