A system for protecting a child on a baby seat of a bicycle, * the baby seat including a seat bottom and a seat back delimiting a receiving space oriented in a longitudinal direction to receive the child, * the baby seat having an outer surface which is opposite to the receiving space, ■ the protection system comprising: - a support configured to be mounted on the outer surface of the seat back of the baby seat, this support comprising a system for removable fastening to the baby seat, - a protection device comprising an inflatable protection structure (26; 26') which is mounted on the support, wherein the protection device has: • as long as no accident situation is detected, an inactive state in which the protection structure (26; 26') is deflated and folded onto the support, • when an accident situation is detected, an active state in which the protection structure (26, 26') is inflated, so as to at least partially surround the receiving space about a structure axis which is substantially perpendicular to the seat bottom, ■ the protection system being characterised in that the removable fastening system comprises: → a hood configured to be slipped onto an upper portion of the seat back which is opposite to the seat bottom, -+ and a tensioning device configured to tension the hood on the upper portion of the seat back. * the baby seat including a seat bottom and a seat back delimiting a receiving space oriented in a longitudinal direction to receive the child, * the baby seat having an outer surface which is opposite to the receiving space, ■ the protection system comprising: - a support configured to be mounted on the outer surface of the seat back of the baby seat, - a support configured to be mounted on the outer surface of the seat back of the baby seat, this support comprising a system for removable fastening to the baby seat, - a protection device comprising an inflatable protection structure (26; 26') which is mounted on the support, - a protection device comprising an inflatable protection structure (26; 26') which is mounted on the support, wherein the protection device has: • as long as no accident situation is detected, an inactive state in which the protection structure (26; 26') is deflated and folded onto the support, • when an accident situation is detected, an active state in which the protection structure (26, 26') is inflated, so as to at least partially surround the receiving space about a structure axis which is substantially perpendicular to the seat bottom, • as long as no accident situation is detected, an inactive state in which the protection structure (26; 26') is deflated and folded onto the support, • when an accident situation is detected, an active state in which the protection structure (26, 26') is inflated, so as to at least partially surround the receiving space about a structure axis which is substantially perpendicular to the seat bottom, ■ the protection system being characterised in that the removable fastening system comprises: → a hood configured to be slipped onto an upper portion of the seat back which is opposite to the seat bottom, -+ and a tensioning device configured to tension the hood on the upper portion of the seat back. → a hood configured to be slipped onto an upper portion of the seat back which is opposite to the seat bottom, -+ and a tensioning device configured to tension the hood on the upper portion of the seat back.