If you set all other considerations aside, most daycares that offer infant care will accept little enrollees once they're able to latch on to a bottle. For many families, though, there are other considerations to take into account when determining when it's the right time for daycare.
Not every new parent is going to have the chance to make child care decisions based only on what’s right for their child's individual needs, but even if you do have the chance, it can be hard to find any kind of consensus about timing. After all, recommendations for the age to start child care range from 6 months to 5 years, depending on the authority doing the recommending, and all sides claim scientific and developmental evidence.
Daycare is definitely a necessity for many parents, and if it's necessary for your family, no time is too early for daycare. Plus, putting your baby in child care could give her a head start socially, although that social experience can definitely still happen outside of daycare.
However, a 2010 study by the Society for Research in Child Development shows that children in full-day child care can experience an increase in the stress hormone cortisol. Even if your child doesn’t show signs of stress while they are in child care, if they get upset when you come to pick them up, it could be a sign that the time they spend there is increasing their stress rate.
The truth is, different children react to situations differently, and there are some children who thrive on social situations at an early age. For others, though, being put in such a social environment earlier than they're ready for can raise their level of stress. One of the major findings of a 15-year study by the National Institute of Child Health and Human Development, however, showed that children who were cared for just by their parents throughout their pre-kindergarten years did not develop differently from children who were also cared for by non-parents.
The NICHD study only looked at a specific group of over 1,000 children put in childcare at 6 months, but it does show a pattern: the places where negative effects start showing up are in poor quality child care, excessive hours in child care, and in quality of home-life.
What this means, essentially, is that babies who aren't being well-cared for, both inside of daycare and out, show signs of stress, and babies who are being well cared for don't. If you provide a positive and supportive home life, and look for a daycare that's a great fit for your baby, she should do just fine, inside of daycare or out.