In the evening when he first met Anna (at home, he'd been in nursery during the day so I was out of hospital by the time he came home), Seb (21 months) was quite curious. Can't really remember to be honest but we have photos of her on my lap and Seb looking at her.
The following morning though I think he'd completely forgotten. I had Anna in the bathroom in the baby chair, screaming, and tried to get him in to change him, but he kept looking at her screaming and backing out, looking a bit scared. I had to take Anna out of the bathroom to get him to come in.
Within a couple of weeks I'm sure he couldn't remember life had ever been any different.