It is permissible to give voluntary charity to rich people, and there is no difference of opinion among the scholars concerning that. The one who gives it will be rewarded, but it is better to give it to one who is in need of it.
Al-Nawawi (may Allaah have mercy on him) said: It is permissible to give voluntary charity to rich people, and there is no difference of scholarly opinion on that. It is permissible to give it to them and the giver will be rewarded for it, but it is better to give it to one who needs it. Our companions said: It is mustahabb for the one who is rich to refuse it, and it is makrooh to offer it to him … it is not permissible for a rich person to take voluntary charity pretending to be poor. End quote from al-Majmoo’ (6/236)
Ibn Qudaamah (may Allaah have mercy on him) said: Everyone who is forbidden to accept obligatory charity, such as the rich, relatives of the giver, kaafirs and so on, is permitted to receive voluntary charity.
End quote from al-Mughni (2/276).
It is mustahabb to give voluntary charity to orphans, even if they are rich, and that is to console them for the loss of their father. As for the obligatory charity (zakaah), it is not permissible to give it to orphans unless they are among the people who are entitled to zakaah, as mentioned in the verse in which Allaah says (interpretation of the meaning):
“As-Sadaqaat (here it means Zakaah) are only for the Fuqaraa’ (poor), and Al‑Masaakeen (the poor) and those employed to collect (the funds); and to attract the hearts of those who have been inclined (towards Islam); and to free the captives; and for those in debt; and for Allaah’s Cause (i.e. for Mujaahidoon — those fighting in a holy battle), and for the wayfarer (a traveller who is cut off from everything); a duty imposed by Allaah. And Allaah is All-Knower, All-Wise”
For more information on these categories of people, please see the answer to question no. 46209.
If the children asked about here do not have enough, from their own wealth or what their brothers spend on them, then it is permissible to give zakaah to them.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: But there is something we should pay attention to here, which is that some people think that orphans are entitled to zakaah in all cases, but this is not so. Orphans are not among those who are entitled to take zakaah, and the orphan has no right to zakaah unless he is among the eight categories of people who are entitled to zakaah.
But as for his simply being an orphan, he may be rich and have no need of zakaah. End quote from Majmoo’ Fataawa Ibn ‘Uthaymeen (18/353).
He also said: We should note that zakaah is not for orphans. Zakaah is for the poor and needy, and the other categories mentioned. An orphan may be rich, his father may have left him enough wealth to suffice him, or he may have an income from social security etc which makes him independent of means.
Hence we say: The orphan’s guardian should not accept zakaah if the orphan has sufficient wealth.
As for charity, it is mustahabb to give it to orphans even if they are wealthy. End quote from Majmoo’ Fataawa Ibn ‘Uthaymeen (18/307).
And Allaah knows best.