"I see them play soccer."
OR
"I see them playing soccer."
Is there a difference between these two?
*****
NOT A TEACHER *****
(1) Here are two sentences that
may shed some light on the
matter. Many teachers use these two sentences.
I saw Tom
cross the street. = I saw him walk completely
across the street.
I saw Tom
crossing the street. = I saw him in the street,
but I do not know whether he actually finished the action.
(Maybe I had stopped paying attention to him because something
else attracted my attention and I turned my head away.)
*****
In your two sentences, probably the past would be more
common:
I saw Tom
play soccer yesterday. = You went to the soccer
field and watched the game.
I saw Tom
playing soccer yesterday. = You walked by the football
field yesterday and just happened to see Tom in action. But you
may have quickly continued on your way.
*****
NOT A TEACHER *****