Therapies that insert genes, inactivate malfunctioning genes, or alter gene expression have marked therapeutic potential for diseases of childhood. Two recently approved treatments for infantile-onset spinal muscular atrophy type 1 (SMA), which was previously uniformly fatal in early childhood, can increase survival among children. Potentially transformative genetic therapies are in the pipeline for Duchenne muscular dystrophy, sickle cell disease, and cystic fibrosis, among other conditions.