While the idea proves to be a lot of fun and quite intriguing, it’s not recommended that children be allowed to use an adult sized massage chair. Massage chairs are designed in proportion to the average human (adult) body. There are rollers and pressers in specific places to correspond with the adult anatomy. There are neck rollers where the neck would be, and thigh rollers where the thighs would fit, etc. A child would obviously not fit into this anatomical bracket. Their necks might sit where an adult’s lower back sits, and these rollers aren’t necessarily designed to be gentle enough to massage a neck. For this reason, it becomes unsafe to subject a child to an adult massage chair. There is risk of strain or injury due to the rollers no lining up to the correct vertebrae or limbs. Significantly taller children might be able to get away with enjoying a massage or two. If their limbs seem to somewhat align with the layout of the chair, then there will be less risk of strain.
Tip: keep the massage function on the lowest level of intensity whenever a child is making use of the chair.