Is there a safe trampoline for kids?

No, at least not those designed for home use neither the big ones for backyards nor the little ones put indoors. The only safe way to use a trampoline is in an athletic facility with the trampolinist hooked into a harness that a certified athletic trainer can yank upward if the athlete is about to fall and with spotters scattered around the edge to push the jumper back toward the center if he or she is about to fly off the device entirely.