A children's high chair comprises a supporting frame (11,111) for a high chair (12,112) for receiving the child. The frame (11,111) comprises in turn a pair of legs (14,15) openable compasswise and with lower ends (19,119) for resting on the ground and stiffening crosspieces (20,120) arranged on both sides of the frame and movable between a non-operational position allowing closing of the frame and an operational position in which the crosspieces engage the legs to hold them steadily in open position. The crosspieces (20,120) can be moved to another more lowered operational position to rest on the ground to constitute high chair rocking members. Advantageously an automatic battery-powered mechanical rocking device can be provided.