Did I make the right choice?

Back in September I stopped working as a nanny after caring for twins, Zachary and Kiera, for the previous 16 months. I started watching them when they were 3 months old and spent about 50 hours with them each week. I met all their basic needs (fed, changed, played with, cared for, and loved them), went to all their doctor appointments with them, took them to their baby enrichment classes and library story time, and saw many of their milestones. I felt Kiera's first tooth, saw Zach roll over for the first time, and I was the one who they both took their first steps to. I was the one they came to when they got hurt or wanted to be loved on. I spent more of their waking hours with them each week than their parents did. They were super attached to me and I was really attached to them. I was the only one, besides their parents, that they let hold them without crying.
In August I decided I was ready for something more challenging and intellectually stimulating, and began applying to other jobs. I was quickly hired and began working with autistic children in September. At the time I was tired of spending all my time with babies, the pay wasn't great (about $10/hour), I wanted more flexible hours, etc. And for the first couple months I was glad with the choice I had made. I went and saw the twins (and Thasia and Joshua) in November. It was wonderful seeing them, but it was bittersweet at the same time...I was no longer the one they went to when they needed a cuddle, they had met milestones that I hadn't seen and gotten taller and older, and I was replaced by a new nanny. And then a couple weeks ago I babysat the four kids for the day. It was wonderful and so much fun. And it made me realize just how much I miss them. I am no longer an integral part of their lives. And that makes me sad.
I enjoy working with the autistic kids I have as clients, and can see the difference I am making in many of their lives. But I miss my twins. A lot.