( ( Have ( ( the children ) ( ( make ( a ( water molecule ) ) ) ( from ( ( ( two ( hydrogen atoms ) ) and ) ( one ( oxygen atom ) ) ) ) ) ) ) . )
(ROOT (S (VP (VB Have) (S (NP (DT the) (NNS children)) (VP (VB make) (NP (DT a) (NN water) (NN molecule)) (PP (IN from) (NP (NP (CD two) (NN hydrogen) (NNS atoms)) (CC and) (NP (CD one) (NN oxygen) (NN atom))))))) (. .)))
Have the children make a water molecule from two hydrogen atoms and one oxygen atom.
(ROOT (S (NP (NP (CD 2) (NN hydrogen)) (, ,) (NP (CD 1) (NN oxygen) (NNS atoms))) (VP (VBP combine) (S (VP (TO to) (VP (VB make) (PRT (RP up)) (NP (NP (DT a) (NN molecule)) (PP (IN of) (NP (NN water)))))))) (. .)))
2 hydrogen, 1 oxygen atoms combine to make up a molecule of water.