It is narrated from Sayyiduna Abdullah bin Ja'far (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) mounted a boy from Banu Hashim and Ibn Ja'far on a camel.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13797
Sayyiduna Abdullah bin Ja'far (may Allah be pleased with them both) relates that whenever the Messenger of Allah (peace and blessings be upon him) returned from a journey, the children of his household would come out to receive him. Once he (peace and blessings be upon him) returned from a journey, and I was sent to him ahead of the others, so he (peace and blessings be upon him) seated me in front of him. Then one of the two sons of Fatimah (may Allah be pleased with her) was brought, and he (peace and blessings be upon him) seated him behind him. Then we entered Madinah, three of us on one mount.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13798
Something similar to this hadith is also narrated from Sayyiduna Abdullah bin Ja'far (may Allah be pleased with them both) from the Prophet (peace and blessings be upon him).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13799
It is narrated from Sayyiduna Abdullah bin Ja'far (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) mounted a boy from Banu Hashim on a riding animal.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13800