Children's Hajj

Hajj is not obligatory on children. However, if they perform Hajj, it will be valid but does not exempt them from performing the obligatory Hajj.
Once, a woman brought a boy to Allah's Messenger (peace be upon him) and asked, "Would the Hajj of this boy be valid?" He said, "Yes, and you will have a reward for doing so." Jabir (may Allah be pleased with him) said, "When we performed Hajj with Allah's Messenger (peace be upon him), we had our women and children with us. We pronounced Talbiah and threw pebbles on behalf of our children."

If children perform Hajj, it will be obligatory for them to perform Hajj again when they attain puberty. Likewise, if a slave performs Hajj and then gains his freedom, he will have to perform Hajj again if he is able to finance the journey.

Ibn `Abbas (may Allah be pleased with the son and his father) reported that the Prophet (peace be upon him) said, "If a boy performs Hajj and then attains puberty, he should perform Hajj again. And if a slave performs Hajj and then gains his freedom, he should perform Hajj again."

If the child reaches the age of discretion, he can enter the state of Ihram and perform the rituals of Hajj alone. Otherwise, his guardian can perform the rites on his behalf, pronounce Talbiah, circumambulate with him, run between Safa and Marwah, stand at `Arafah, and throw the pebbles on his behalf.

If he attains puberty before standing at `Arafah or during it, he will not have to perform Hajj again
Malik maintained that this Hajj will not suffice the child, while the Hanafis held that it does suffice him if he renews his Ihram after attaining puberty.