The children were entrusted ___ the care of their uncle.

Explanation: Entrust: to give someone a thing or duty for which they are responsible.

Entrust Subject with Something -
Many people had entrusted the company with money they intended to use in retirement.
Be entrusted with something/somebody - I was entrusted with the task of looking after the money.

Entrust Something to Subject -
He entrusted the arrangement of a mortgage to a local firm of financial advisers.
Government has been entrusted with elected politicians.

Entrust Subject to do Something -
We entrust a board of Edinburgh's leading businessmen to run the affairs of the organization.

উপরের উদাহরণগুলো বিশ্লেষণ করলে বুঝা যায় এখানে শূন্যস্থানে to বসাতে হবে। 

Source: Cambridge Dictionary