Birth order may have another impact: a new study finds kids who have older siblings are more likely to have breathing problems than kids who are the oldest or only children.

Kids with at least two older siblings were 50% more likely than their peers to have been hospitalized for respiratory issues.

Experts think younger kids might simply be exposed to more respiratory infections at an earlier age.

The birth order association was only significant when the child did not have other allergies or a parent with asthma.

In other medical news…

Swimming season is just around the corner, and a new study from the EPA and Centers for Disease Control and Prevention finds kids under 10 are most at risk for swimming-related stomach illnesses.

Researchers tested the water quality at 4 great lakes beaches, and then followed up with swimmers 10 to 12 days after their visit.

Those under age 10 were most likely to get sick from the bacteria found in the water.