Sulayman bin Yasar (may Allah have mercy on him) says that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) married his young son to his niece, and his son was young at that time. This is to be understood as his brother having concluded the contract and his uncle having accepted it on behalf of his son because of his being young.
(b) Al-Hasan (may Allah have mercy on him) narrates from the Prophet (peace and blessings be upon him) with a weak chain: "When a man marries off his son and he dislikes it, there is no marriage; and when he is married in childhood, it is permissible."
(c) Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says that the dower is the responsibility of the child whom you are marrying off.
(d) Ata (may Allah have mercy on him) says that when a man marries off his young child, his marriage is permissible and there is no divorce (for him).
(e) Imam al-Zuhri (may Allah have mercy on him) says that the divorce of an insane person is not permissible.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13817