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 (L) 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 is inflated, so as to at least partially surround the receiving space about a structure axis (A) 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 (L) 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 is inflated, so as to at least partially surround the receiving space about a structure axis (A) 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 is inflated, so as to at least partially surround the receiving space about a structure axis (A) 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 . <EOS>