"A small child can become nervous if it is not allowed to laugh."
Translation:Ett litet barn kan bli nervöst om det inte får skratta.
To substitute 'a child' for the pronoun 'it' is not correct in English. The pronoun "it" is used for inanimate objects or animals, not for persons. He or she are the appropriate substitutions for a person. The one exception is 'baby', where 'it' is acceptable, if one does not know the gender of the baby.