I started daycare when my oldest was about 10 months old. She did amazingly well. My first little guy was the same age and he became her best friend. I quickly discovered she didn't need her Mommy as much as I thought she did

I took 6 months off when my second was born and she too did an good job transistioning into daycare and I even had another 6 month old in care too. I will be the first to admit that my 2nd as an infant HATED to be held, so she naturally didn't need a lot of attention.

I don't know if having another child the same age starting daycare with them was the key or if they would have did well with any age.

My girls as a result of daycare had friends to play with and didn't need me as much. They even had no issues with sharing my attention. Well, there was one exception and that is when I was doing 24 hour / 7 days a week childcare and my oldest at 9 did get upset with me always having other children in the house and so I quit working the extended hours for her and haven't had any problems since.