I have 5 children, the oldest being an 11yr old boy who has Autism. My problem my autistic boy has problems socializing and seems only be socializing at school with non-Muslim girls. I try to discourage it as with the younger ones who understand quite well and are happy to please Allah by segregating when possible. My older boy wants to bring one of the girls home. To make things extra complicated this girl friend has a terminal disease which makes her age much faster than other people and may only have a few years left (Allahu Alim). I am worried about him reaching maturity and not having segregation instilled in him at an earlier age as he has a learning problem as well and it does take time for him to learn things. I am also worried that this may hamper his ability to socialize if I prevent him from socializing with the only friends he has because they are girls. Please if you could give me some advice and if possible some Islamic rulings on this as I do want them to learn to please Allah I am not sure how to handle this situation.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be
upon our Prophet Muhammad and upon all his Family and Companions.
It is a mistake to let children study in mixed schools. Naturally they
develop a habit of talking with girls and socialising with them which is
forbidden or at least leads to Haram.Sometimes an eleven year-old boy becomes mature and then he becomes responsible for his deeds and actions according to Sharia.If it is supposed that he still did not mature, at least he becomes accustomed to befriend girls in this stage of life. Therefore, he finds it difficult to give up this practice after becoming mature.It is not permissible to bring the girl to your home to sit with your boy regardless of how miserable her condition is.
We advise you to visit religious Muslims and ask them to visit you, through these mutual visits your boy will befriend others and thus he will develop the friendship of boys and good Muslims. It is also recommended to take him to mosques to socialize with Muslims. Do not spare any efforts to have your children memorize the Qur'an and to teach them religious matters. Seek help from Muslim scholars to guide your children to the right things and warn them of the bad sequences of befriending girls or women. The scholars may also explain to them the merits of chastity and virtuousness and that the Sharia demands Muslim men and women to lower their gaze and should not look at marriageable women. Islam also prohibits shaking hands with such women, etc.
Without delay you have to teach your children what is mentioned here before it is too late.
Turn towards Allah asking His Help and make supplication as much as possible to cure your children and protect them from all misfortunes.
Allah knows best.