My daughter was 4 when I went back to work full-time (not in daycare) after a year's mat leave. Although she had been in daycare prior to my mat leave, she had certainly become accustomed to being at home with me. I honestly think the adjustment was harder for her at age 4 then it was when she was 1 years old and just starting out. But it was only really bad for the first few days and then she was mostly just shy and unsure. Once she got to know the daycare provider and the other kids better, she settled right in. All in all, it was about 2 weeks of adjusting.

For my own daycare now, I just assume that most kids will need a couple weeks to adjust no matter how old they are.