EDIT: I was thinking you wanted someone for full-day care. A couple of hours after school is different. Finding someone who is reliable, safe, experienced and capable of helping with homework is great! No, I don't regret leaving our former sitter, but I sure do miss her!
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We recently (as in yesterday) transitioned my son from an in-home daycare to a preschool center. We had many reasons and second-guessed ourselves right up until my husband picked him up yesterday. He was grinning ear-to-ear and asked if he would get to come back. Whew.
It really depends on why you decided to leave your sitter. For us, there were many reasons. Some were educational- my little guy is really ready for more structured learning and had mentioned that he wanted to read more books and do more numbers than they were doing. Some were logistical- the daycare is 30 minutes out-of-the way for my husband and she closes quite a bit for vacation, which is really not possible for us any more. Regardless, it was a difficult decision and one that we really thought about before making a final choice.
We also had something really great to "go to" before we left the other situation. That may be part of your concern here. She has good ELA skills- great. That doesn't mean squat when it comes to childcare!
Before you agree to something long-term, have a two week trial period. Have her come for a few hours and see how your children do with her. See how she does with them. If she's not "the one", you will know very quickly!