Children must  do their own work. 
( Children ( ( must ( do ( their ( own work ) ) ) ) . ) )
(ROOT (S (NP (NNP Children)) (VP (MD must) (VP (VB do) (NP (PRP$ their) (JJ own) (NN work)))) (. .)))
Many children are put to work for the first time in school.
( ( Many children ) ( ( are ( put ( to ( work ( for ( ( the ( first time ) ) ( in school ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Many) (NNS children)) (VP (VBP are) (VP (VBN put) (S (VP (TO to) (VP (VB work) (PP (IN for) (NP (NP (DT the) (JJ first) (NN time)) (PP (IN in) (NP (NN school)))))))))) (. .)))