Fill up the ward (6)
I believe the answer is:
charge
I believe this clue is a double definition.
'fill up' is the first definition.
(charging is a kind of filling up)
'ward' is the second definition.
(both can mean a child in someone's care)
'the' is the link.
(Other definitions for charge that I've seen before include "Fill; fee" , "person in custody" , "Race to attack" , "Keeping" , "Accuse; load, fill" .)