Why is an infinitive used here?

I was studying my flash cards and came across the sentence:  "Mi piace guardare i miei figli giocare gli sport."  ("I like to watch my sons play sports" is my intended translation).

I can't remember why "giocare" is supposed to be the infinitive form here instead of using "giocano."  I did several variations of this sentence in Google Translate without the verbs piacere, guardare, and giocare, and the results always came back with the infinitive (e.g. "I watched my sons eat pasta" -  "Ho visto i miei figli mangiare pasta.")  Why is it that the last verb is supposed to be infinitive form?  I can't remember the rule for the life of me!

 Thanks,

Jay

Hi Jay,

When infinitives such as guardare (to look at), vedere (to see), sentire (to hear) etc. are followed by another sentence, the verbs in it are not conjugated. This happens in English as well:

Mi piace sentire mia sorella cantare. I like to hear my sister sing.
Mi piace sentirla cantare. I like to hear her sing.
Voglio vedervi fare i compiti! I want to see you (pl) do your homework!
Mi piacerebbe vederli fare i compiti. I'd like to see them do their homework.

Hope this helps!

Lucia
 

Thanks, Lucia.  That does help. 

I do have a follow up though - What about when there is no infinitive?   (e.g. "I watched my sons eat pasta" -  "Ho visto i miei figli mangiare pasta.")  

Thanks,
Jay
 

Hi Jay,

The rule actually applies in this case as well, and the good news is that English works the same way!

I came up with another example: lasciare (to let, to leave), as in:
Non la lascio andare. I won't let her go. (not "goes")
Or fare:
Non ti faccio guardare la tv. I won't let you watch the tv.

Hope this helps!

Lucia

Thanks Lucia!