Another way, besides OR, to increase the number of search results is to use truncation. This will find all words that have the same root or trunk.
child* = child, children, childish, child's, childhood, children's, etc.
Databases use many different symbols for truncation, so remember to check the search tips. EbscoHost and ProQuest databases use the * (asterisk):
child* = child, children, childish, child's, childhood, children's, etc.
Nexis Uni uses the ! (exclamation mark):
child! = child, children, childish, child's, childhood, children's, etc.