Answered by Shaykh Ilyas Patel
1) does a child who is over 7 but not yet matured lift the state of khalwa in the hanafi school? i.e a adult man and woman alone together with this third child.
2) is a place which people commonly pass khalwa e.g a reception area where the door however is closed?
In the name of Allah Most Compassionate Merciful
A1
A child will not act as a barrier for a man and woman and their state of being together will not be lifted. The child does not act as a barrier or like defence for the man to go near the woman.
It is mentioned in Radd al-Muhtar as follows:
What the gist of the discussion is that the forbidden seclusion is negated due to a barrier, presence of a mahram or a trustworthy woman who is able…
(Radd al-Muhtar,Allama Ibn Abidin, pg 368 V.6)
A child does not have the physical or emotional drive to stop the man from going nearer to the woman, thus if a child is the third person present in a man and woman seclusion it will not act as a barrier.
A2
If people are in the building or living in the house and a non-mahram man and woman pass in a hallway or reception area then it will not be a seclusion as they are just passing by and it is not considered a room.
And Allah knows best