Offering Salah alone behind the congregational rows
If a person who wants to offer Salah finds a complete row, he should wait until another one comes to form a new row with him. He should not pull anyone from the existing row. If he can join the row or stand to the right of the Imam, he should do so. As for standing with the young boys, it can be done if they are old enough. It was reported in
the Two Sahih (authentic) Books of Hadith (i.e. Al-Bukhari and Muslim)
and others from
Anas (may Allah be pleased with him) that he said,
The orphan and I aligned behind him and the old lady stood behind us.
He was referring to the Messenger of Allah (peace be upon him) when he visited them one day. If the boys are not old enough, it is considered as if he is offering Salah individually, which is invalid, The Prophet (peace be upon him) stated,
The Salah of a person standing alone behind a row is invalid.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.