Transitioning son from beloved day care provider

My son has been in a small home-based day care since he was 4 1/2 months old, about 30 hours a week. He is now 21 months, and we are beginning to think of moving him to a new day care sometime this summer or fall. We have moved and it will become logistically very challenging to keep him there when I have baby #2 in August. Also, I think he is ready for something a little more developmentally oriented.

The problem is - he absolutely adores his caregiver. She's great. All her kids are quite attached to her, but my son seems more attached than any of the others - which I hope is evidence that he feels secure in relationships, as he is also attached to Mom and Dad. We think of her almost as a third parent. The problem is, of course, she's not, and she will not always be a part of his life. I am worried about the impact it will have on him to ''move on'' from her. He will probably see her now and then for the next several years, but not four days a week. I guess this is the flip side of the perfect day care situation. I'm also wondering whether it would be better to transition him well before the new baby arrives. How has it gone for other parents transitioning their child from a special care provider? Am I worrying too much? worried