Response: Regarding the mahram, the Scholars have mentioned that two conditions must be met:
1) The coming of age (puberty);
2) Mental awareness.
So, whoever has not yet attained puberty then it is not correct for him to be a mahram; and whoever is not yet mentally aware then it is not correct for him to be a mahram since the intent behind the (presence of a) mahram is protection of the wife and maintaining her and preventing any attack upon her. (Clearly) the young child is unable to undertake any of these (roles).
So I say, now the woman – as per the question – has reached her destination, so she is not to return to her husband until he comes and collects her and takes her (back) with him. Alternatively, she can travel with one of her mahrams (father, brother, etc.) – from amongst those who have attained puberty and are mentally aware. As for the young child who is nine years of age, then he cannot be her mahram.
Shaykh Ibn ‘Uthaymeen
I’laam al-Mu’aasireen bi-Fataawa Ibn ‘Uthaymeen – Page 369. fatwaonline.com