Your sentence is almost perfect! Here's the original sentence:
With an ant farm, we get to watch the life of ants.
It is grammatically correct, but to make it sound a little more natural, you can say:
"With an ant farm, we get to watch the lives of ants."
Why? Because ants is plural, so we say lives (plural) instead of life (singular).
Another way you could say it is:
"With an ant farm, we get to watch how ants live."
This means we can see what ants do in their daily life.
Great job noticing that an ant farm helps us watch ants!