Assalaamu `alaikum warahmatullaah.
Before getting into your question, you should know, akhi, that present-day adoption was something that was practiced during jaahiliyyah and also in the early days of Islam. In the adoption process, the child gains your name and loses his/her father's name, which, as we know, is not permissible. Allah `azza wa jalla says in soorat al-Ahzaab "Call them by the names of their fathers." (
أدعوهم لآبائهم )
It was narrated from Abu Dharr (may Allaah be pleased with him) that he heard the Prophet (peace and blessings of Allaah be upon him) say: “There is no man who knowingly calls himself after someone other than his father but he has committed kufr. Whoever claims to belong to people to whom he has no ties of blood, let him take his place in Hell.”
(Narrated by al-Bukhaari, 3317; Muslim, 61)
Also, later when the child grows up, your biological children will consider him/her their real sibling and it won't be allowed for them to marry one another and that's not permissible.
Sponsoring an orphan is allowed and very much encouraged. In a hadeeth, narrated by Sahl ibn Sa`d, the prophet
said,
“I and the one who sponsors an orphan will be like this in Paradise” – and he gestured with his index and middle fingers, holding them slightly apart.
(Narrated by al-Bukhaari, 4998)
You can bring an orphan child to come live with you in your house in order to sponsor them but once the child become reaches puberty, you should separate them from the rest of the household (the boy from the girls/women and the girl from the boys/men).
I have been thinking about this. There are so many orphans in the world today and yet people are producing more children. Which one is better according to Islam, to have an own child or to adopt a child?
Should we not start to take care of the children that already exist in the world rather than wanting new ones?
There's good in both having children and helping orphans. But I don't think it's a matter of choosing one or the other. Have children if Allaah allows you to but also sponsor orphans to the best of your ability. And by the way, a man providing for his household is a form of sadaqah. So if he's only able to take care of his own kids he still gets rewarded.
And it is encouraged to have lots of kids. The prophet said in a hadeeth, the brother already mentioned it, but his
's words were: "marry those who are loving and fertile, for I will be proud of your great numbers before the other nations."
And it's not permissible to hold of on concieving children for fear of poverty in Islaam. There are many verse in the qur'aan where Allaah `azza wa jalla says that He is the one who provides for everyone.
I have also thought that how can someone want a child except out of blind selfishness. Today we do not have an Islamic country, we can not even guarantee the safety of our children.
How can wanting and conceiving a child be regarded as selfishness? It's a blessing from Allaah and He grants it to some and withholds it from others. And we do have Islamic countries, we just don't have a Caliphate in place.