Your kid will need a fingerprint...

I had the same experience last October. My son was 10 years old. USCIS sent a finger print notice to my son after the approval notice. In the fingerprint appointment, they also took a photo for my son. My son received his card about 1-2 months after the appointment. It should have happened in 1-2 weeks. But USCIS sent his fingerprint results to Vermont Center wrongly because our cases were transfered to Texas center from Vermont. After using a congressman's help, USCIS corrected their mistake and sent us the card quickly.