It is obligatory on you
to keep the orphans' money in your possession until they reach the age of consent and then give them their money. You should also pay Zakah on this money on a yearly basis (Part No. 14; Page No. 261) at a rate of 2.5 % of the total. You should make the best choice in regard to investing this money in a lawful way. It is not permissible for you to lend the orphans' money to anybody. Allah (Exalted be He) says:
And give unto orphans their property and do not exchange (your) bad things for (their) good ones; and devour not their substance (by adding it) to your substance. Surely, this is a great sin.
Furthermore, it is not permissible to invest their money in Riba-bearing (usurious) banks or other institutions. Also it is not permissible to waive anything of an orphan's right, whether part of the Diyah or anything else. You should spend on them from their money to meet their needs. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.