watchful

(a) paying attention to what is happening in case of danger, accidents, etc.

Her expression was watchful and alert.
His mother kept a watchful eye on him.
The children played under the watchful eye of their teacher.
Sedan also provided Les Misérables with its rock quarry, where prisoner Jean Valjean (Dominic West) labours under the watchful eye of Inspector Javert (David Oyewolo). Read more Les Miserables BBC location guide: where was the BBC1 TV series filmed? - Radio Times

Derived words: watchfully, watchfulness

She seemed watchful and slightly worried.
The children organised the activities themselves under the watchful eye of their teacher