Your baby needs to be able to hold her head upright and bear a bit of weight on her legs without assistance in order to successfully use a jumper. It isn’t as much a matter of her age and weight as it is her development. However, if your baby is already walking on her own, the jumper won’t probably be of much use or interest anymore. Children who are between the “upright head” and “walking” milestones are the best candidates for a baby jumper.