At the end of the second year, children begin to label their own and others' internal states with words, such as  want,   happy,   mad,   think,  and  pretend. 
( ( At ( ( the end ) ( of ( the ( second year ) ) ) ) ) ( , ( children ( ( begin ( to ( ( ( ( ( ( ( label ( ( ( their own ) and ) ( ( others ' ) ( internal states ) ) ) ) ( with ( ( ( ( words , ) ( such ( as want ) ) ) , ) ( happy ( , mad ) ) ) ) ) , ) think ) , ) and ) pretend ) ) ) . ) ) ) )
(ROOT (S (PP (IN At) (NP (NP (DT the) (NN end)) (PP (IN of) (NP (DT the) (JJ second) (NN year))))) (, ,) (NP (NNS children)) (VP (VBP begin) (S (VP (TO to) (VP (VP (VB label) (NP (NP (PRP$ their) (JJ own)) (CC and) (NP (NP (NNS others) (POS ')) (JJ internal) (NNS states))) (PP (IN with) (NP (NP (NP (NNS words)) (, ,) (PP (JJ such) (IN as) (NP (VP (VB want)))) (, ,)) (ADJP (JJ happy) (, ,) (JJ mad))))) (, ,) (VP (VB think)) (, ,) (CC and) (VP (VB pretend)))))) (. .)))
Children think a lot about their internal states and the internal states of others. 
( Children ( ( think ( ( ( ( a lot ) ( about ( their ( internal states ) ) ) ) and ) ( ( the ( internal states ) ) ( of others ) ) ) ) . ) )
(ROOT (S (NP (NNP Children)) (VP (VBP think) (NP (NP (NP (DT a) (NN lot)) (PP (IN about) (NP (PRP$ their) (JJ internal) (NNS states)))) (CC and) (NP (NP (DT the) (JJ internal) (NNS states)) (PP (IN of) (NP (NNS others)))))) (. .)))