It doing back refer by the rounded kids through perch .
(ROOT_0 (S_0 (ATS_3 (NP_1 (PRP_0 It)) (VP_4 (ATVP_1 (VBG_0 doing) (PRT_0 (RP_0 back))) (VP_5 (VBP_0 refer) (PP_2 (IN_0 by) (NP_3 (NP_6 (ATNP_1 (DT_0 the) (JJ_1 rounded)) (NNS_1 kids)) (PP_0 (IN_1 through) (NP_5 (NN_3 perch)))))))) (DOT_0 .)))