Parents have long anguished over whether they should send their preschool kids to day care, and thus far, the mixed bag of research hasn't been much help. Some studies show that day care boosts academic performance, while others say toddlers have fewer behavioral problems if they stay home. For parents, the should-we-or-shouldn't-we decision only got tougher in July when a paper published in the Archives of Pediatric and Adolescent Medicine found that over a nine-month period, babies in day care gain 0.4 lb. more than those who stay home. The researchers — who studied more than 8,000 9-month-olds — suspect that infants in day care are heavier than those cared for by a parent because they have less structured eating habits. Sometimes weight gain can be a good thing for infants who are underweight, but for others, it could be a risk factor for developing childhood obesity.