They were more likely to look insecure in their relationships to their mothers, in particular at the end of their first year of life. Unfortunately most parents are unaware of this growing research. Bonding takes place in the hours and days following birth, usually between the mother and the child. Bonding demands consistency, and day care interrupts that consistency especially when there is not one person providing the primary care for the child. Children placed in a day care center too early are deprived of a primary care giver and will manifest psychological problems.
Personality development is another concern.
Most children will get off to a better start in life if they spend the majority of their waking hours during the first three years being cared for by their parents and other family members rather than in any form of substitute care. A final concern is the negative effect of substitute care on a child. Jean Piaget has shown that children are not capable of reflective thinking at young ages. For example, they do not have a concept of object permanence. If you hide a ball, the infant will stop searching for it because it has ceased to exist in the child's mind.