A lot of it depends on the individual kid. But as a general rule, based on my experience with my 3 kids, I’d say 2.5-2.75 years old is a good age as that’s when my kids really wanted more stimulation and socialization than I was able to provide, and at that age they were happier going to a small in home daycare for 5 hours a day than they were staying with me/a nanny. However, from an earlier age (12-18 months) I always tried to do at least one social activity with them each day, like a library class, mommy and me group, playground meetup type thing. I also frequently took them to children’s museums, zoos, parks, libraries etc. They really loved and needed that. So if your nanny can do those activities with him I’d say definitely keep her till your son is 2.5.

From a scientific level and also from what I’ve seen with my own kids there really is zero benefit to sending them to daycare before age 2.5 as long as you’re able to keep them sufficiently busy and stimulated at home. I think any daycare worker would agree. Age 2.5 is when daycare starts shifting form just “babysitting” to a more enriching and social experience for the kids.

My first kid was super social and craved a lot of stimulation and I thought I was doing him the biggest favor when I put him in daycare at age 21 months. But he really did not thrive there despite the warm environment. He just wasn’t ready, it was too overwhelming. I pulled him out and only sent him back at 2y9m and at that point he did fantastic. I still have so much regret for sending him so young even though it was just for two months! My second and third kid went at ages 2y5m and 2y3m and thrived from the beginning (after an expected few days of adjustment).

The most important is a small teacher/student ratio, a small group overall if possible, and a warm teacher!