The longer children spend in group daycare, the more aggressive and disobedient they are throughout primary school, even if they attend a high-quality setting, according to new research. The findings are from one of the largest and most comprehensive studies on the effect of early childcare that has followed 1,364 children from birth in the United States. The study found that both positive and negative effects of experiences in the first four or five years of life are evident at the age of 11.