Hi Missy, My DD had squint surgery back in May, although not at Moorfields. It is a little scary for the parents but the actual surgery was just over an hour from taking her in for her anaesthetic to her coming around. They cut into the muscles and straightened the eyes (she had bi-lateral squint repair, so both eyes).
The worst of it was seeing her go under the general anaesthetic, so prepare yourself for that as it is medically absolutely fine, but a little frightening for Mum!
It was done under day surgery, so we went in for 7am, and she was in surgery before 10. The doctors and nurses were excellent. When she came around she was very groggy so we didn't get to go home until 5pm as they won't let you go until your child has been up and walking around, had something to eat etc.
She was uncomfortable with it, but plenty of Calpol and Ibuprofen kept it under control. She was taking pain relief for about a week afterwards and even when she went back to school, when she was tired her eyes got sore. Also the side-effects of the anaesthetic meant she was very tired for a few days (and a little bit out of it!) and also quite emotional and upset. But she was back to her normal self within 2 weeks.
They need to have a week off school to recover. From our perspective it was hugely successful. DD had a severe squint which meant even with her glasses on you could see it. I was told that they can't guarantee how accurate it would be as its tiny changes they are making to the eye, but cosmetically her eyes look perfect now. There is absolutely no squint and we are delighted with the results.
Your child will be absolutely fine. To be honest, I think the op itself is hardest for the parents!!