All perfect praise be to Allah. Blessings and peace be upon Prophet Mohammad and upon his family and companions.
Breaking any of the restrictions of Ihram by a child who is assuming Ihram for Hajj, or Umra, such as wearing form-fitting clothes, or wearing perfume can be clarified as follows:
First: If the child was less than seven years old, then no ransom is due on him/her.
Second: If he/she was seven, or more, but didn`t reach the age of puberty, then the ransom is due from the wealth of his guardian, and if the one who led him/her to break any of the restrictions of Ihram did it unintentionally : out of ignorance, or being oblivious, then he/she isn`t considered sinful.
It was stated in [Moghni Al-Mohtajj] by Alkhateeb Ash-Shirbini: “ If the child violated any of the acts of Hajj, then Hady is due on his guardian who is obligated to stop him/her from breaking the restrictions of Ihram. If the child was seven, or more and he deliberately violated any of these restrictions, then the ransom is due from the wealth of his/her guardian…But, if he/she was less than seven years , then nothing is due on him/her.”
We would like to draw your attention to the fact that the pillars of Umra are concluded with shaving, or trimming the head-hair, so if the violation was committed after the boy had shaved or trimmed his hair, then he gets out of the state of Ihram and nothing is due on him, whether he was seven years old, or less than that. And Allah knows best.