Is the guardian of an orphan's money entitled to invest this money without consulting anyone, and is it permissible for him to own the growing wealth when handing over the principal to the orphans upon their reaching maturity?

It is permissible for the guardian of an orphan or his sole trustee to manage the orphan's wealth in a befitting manner and in a way that is most beneficial to the orphan. All profits shall belong to the orphan. It is also permissible for a poor guardian to partake of the orphan's wealth in a reasonable way.