пока дети играли, их мама наблюдала

пока дети играли, их мама наблюдала за ними

Результаты (английский) 1:

While the children played, their mom was watching them

Результаты (английский) 2:

while the children played, their mother was watching them

Результаты (английский) 3:

while children played, their mother watched them