For US FDA approval, for example, drugs approved for pediatric use are drugs that have been studied and to some degree shown safe and effective in children.
However, many trials and often use of drugs and devices in children is not approved, yet drugs are still used. It is up to physicians to weigh the risks and benefits.
Typically, randomized controlled trials are not performed at high enough power to contrast between safety and efficacy of different drugs unless they are truly extremely different. Therefore, you cannot conclude that a pediatric-approved drug is safer than an unapproved drug merely because it is approved, you can only conclude that no one has paid for a sufficiently large study in a pediatric population to support adding the indication.
Murthy, S., Mandl, K. D., & Bourgeois, F. (2013). Analysis of pediatric clinical drug trials for neuropsychiatric conditions. Pediatrics, peds-2012.
Neville, K. A., Frattarelli, D. A., Galinkin, J. L., Green, T. P., Johnson, T. D., Paul, I. M., & Van Den Anker, J. N. (2014). Off-label use of drugs in children. Pediatrics, 133(3), 563-567.