Less than a week after Christina S. Ballester’s son Alexander was born, he underwent surgery to repair a congenital heart defect.Ballester’s experience with Alexander, now 3 years old and healthy, has motivated her to organize a concert on April 14 in Wilmette benefiting the Children’s Health Foundation, Illinois chapter.“I was very fortunate that they found it early before he was born,” said Ballester, a senior care claims counsel with Medpro Group, a health-care liability insurance company.  …