It is permissible to give voluntary charity to rich people

Firstly: 

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). 

Secondly: 

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”

[al-Tawbah 9:60]

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.