What do you call a child for whom you act as a guardian / custodian?

What is the term for this, if there is such a term?

For example, if you're a parent, you refer to your offspring as a 'child' and the child refers to you as their 'parent'.

I am asking because I need to have a term for the relationship of a guardian to the child. For a child, they can refer to this person as their 'guardian' but the other way around (guardian to child) doesn't seem to have a term.

What should I call it?

Solution 1:

I believe the usual term is 'ward'.

In law, a ward is someone placed under the protection of a legal guardian. - Wikipedia

Solution 2:

The old-fashioned word was charge - i.e. my charge has now come of age.

From OED sense 14.

a. A thing or person entrusted to the care or management of any one. spec. The people or district committed to the care of a minister of religion.

1609 Shakespeare Troilus & Cressida v. ii. 7 Dio. How now my charge. Cres. Now my sweet gardian.

Edit. Having submitted this answer earlier, I am now persuaded that ward is the better word and have up-voted @Kate Bunting's answer.

I no longer think foster son/daughter is correct, since, in the UK anyway, a foster-parent is not the same thing as a guardian. Though one must have regard to the OP's question which refers to guardian/custodian. A foster-parent is more of the nature of a custodian, with day to day control of the child's welfare, but usually under the supervision of a Local Authority, who hold the care order from the Court. It is the Authority who have legal guardianship.

Solution 3:

The legal terms is "ward".

Young Dick Grayson was Bruce Wayne's Ward on the Batman series.