As early as 1 1/2 to 2 years, children begin to talk about the past, guided by adults who prompt them and expand on their fragmented recollections.
( ( As ( early ( ( as ( ( 1 1/2 to ) 2 ) ) years ) ) ) ( , ( children ( ( begin ( to ( talk ( about ( ( ( the past ) , ) ( guided ( by ( adults ( who ( ( ( prompt them ) and ) ( expand ( on ( their ( fragmented recollections ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (JJ early) (QP (RB as) (CD 1 1/2) (TO to) (CD 2)) (NNS years))) (, ,) (NP (NNS children)) (VP (VBP begin) (S (VP (TO to) (VP (VB talk) (PP (IN about) (NP (NP (DT the) (NN past)) (, ,) (VP (VBN guided) (PP (IN by) (NP (NP (NNS adults)) (SBAR (WHNP (WP who)) (S (VP (VP (VB prompt) (NP (PRP them))) (CC and) (VP (VB expand) (PP (IN on) (NP (PRP$ their) (ADJP (JJ fragmented)) (NNS recollections)))))))))))))))) (. .)))
As young as 1 1/2 to 2 years, children will begin to talk about their past when they are guided by adults who will prompt them. 
( ( As ( young ( ( as ( ( 1 1/2 to ) 2 ) ) years ) ) ) ( , ( children ( ( will ( begin ( to ( ( talk ( about ( their past ) ) ) ( when ( they ( are ( guided ( by ( adults ( who ( will ( prompt them ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (JJ young) (QP (RB as) (CD 1 1/2) (TO to) (CD 2)) (NNS years))) (, ,) (NP (NNS children)) (VP (MD will) (VP (VB begin) (S (VP (TO to) (VP (VB talk) (PP (IN about) (NP (PRP$ their) (NN past))) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP are) (VP (VBN guided) (PP (IN by) (NP (NP (NNS adults)) (SBAR (WHNP (WP who)) (S (VP (MD will) (VP (VB prompt) (NP (PRP them))))))))))))))))) (. .)))