Children's Hospitals and Clinics of Minnesota is planning to build a top-level pediatric trauma center, with the help of a $17.5 million gift from UnitedHealth Group Inc. It is by far the largest grant the hospital has ever received and is part of a $150 million fundraising drive by Children's for its new building and accompanying programs. The $17.5 million grant is also UnitedHealth's largest single gift so far under its United Minnesota program, which aims to hand out $100 million over 10 years. Children's expansion comes at a time when competition for kids' health care is intensifying. Fairview is building a new $275 million children's hospital, the University of Minnesota Amplatz Children's Hospital, set to open in March. Meanwhile, two other Minnesota facilities recently received Level 1 pediatric trauma certification, the same level that Children's will seek.