Allah the almighty orders us not to waste the wealth of orphans if we are responsible for them saying:
And give to the orphans their properties and do not substitute the defective [of your own] for the good [of theirs]. And do not consume their properties into your own. Indeed, that is ever a great sin. (4:2)
I do assume that nevertheless if this wealth reaches the nisab zakat is a due on it (let me know if I'm wrong). Further I assume that as long as these orphans are children, unmarried or not yet able to be in charge for themselves, the person who is in charge for them is also responsible on their belongings and wealth (at least not all scholars consider adulthood as a condition for paying zakat).
Who has to pay it?
The person who is responsible for the orphans from his own oney or from their money?
What if this person is wealthy himself is it a good deed to leave the orphans money untouched and spend for them from his own money?