At first, children find it difficult to distinguish words and other mental symbols from the objects and actions to which they refer.
( ( At first ) ( , ( children ( ( find ( it ( difficult ( to ( ( distinguish ( ( words and ) ( other ( mental symbols ) ) ) ) ( from ( ( the ( ( objects and ) actions ) ) ( ( to which ) ( they refer ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN At) (NP (JJ first))) (, ,) (NP (NNS children)) (VP (VBP find) (S (NP (PRP it)) (ADJP (JJ difficult) (S (VP (TO to) (VP (VB distinguish) (NP (NP (NNS words)) (CC and) (NP (JJ other) (JJ mental) (NNS symbols))) (PP (IN from) (NP (NP (DT the) (NNS objects) (CC and) (NNS actions)) (SBAR (WHPP (TO to) (WHNP (WDT which))) (S (NP (PRP they)) (VP (VBP refer)))))))))))) (. .)))
Children are always at ease differentiating words and other mental symbols from objects and actions. 
( Children ( ( ( are always ) ( ( at ease ) ( ( differentiating ( ( words and ) ( other ( mental symbols ) ) ) ) ( from ( ( objects and ) actions ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Children)) (VP (VBP are) (ADVP (RB always)) (VP (PP (IN at) (NP (NN ease))) (VBG differentiating) (NP (NP (NNS words)) (CC and) (NP (JJ other) (JJ mental) (NNS symbols))) (PP (IN from) (NP (NNS objects) (CC and) (NNS actions))))) (. .)))