Question
I went to Hajj and intended to have my young son, who is eight months old, to perform Hajj as well. I forgot to dress him in the Ihraam and no one with me brought this to my attention until when we were in Mina and after me having told them about my intention for his Hajj and (after) we had performed all the actions (thus far). What is the ruling on such a case?

Fatwa
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Whoever does an action that is prohibited in the state of Ihraam involving luxuries such as wearing form-fitting clothes or applying perfume and so on due to forgetfulness or ignorance, then there is nothing due on him. However, he should stop doing such an action once he knows of its ruling or remembers it.

Hence, you are not required to do anything since you removed his form-fitting clothes and clothed him in the Ihraam (clothing of ritual consecration) after being reminded.

Allah Knows best.