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!