(S (S (PP (PP (BASENP (NN 少年) (NN たち)) (IN に)) (IN は)) (COMMA 、) (S (PP-SBJ (NP (S-REL (PP (NP (PP (BASENP (NN 刺傷) (NN 事件)) (IN の)) (NN 時)) (IN に)) (S-NSBJ (VP (PP (BASENP (NN 家)) (IN に)) (VP (VBO い) (VP (MDV なかっ) (VP (MD た))))))) (NP (PP (BASENP (NN ３) (NN 歳)) (IN の)) (NN 妹))) (IN が)) (VP (VB いる)))) (PERIOD 。))
少年 たち に は 、 刺傷 事件 の 時 に 家 に い なかっ た ３ 歳 の 妹 が いる 。
The boys have a 3-year-old sister who was not home at the time of the stabbing .