Query the pages with the properties of child node

SELECT * FROM [cq:Page] AS page WHERE ISDESCENDANTNODE(page ,"<<Parent folder of pages>>") AND [jcr:content/<<child node name>>/<<child node property>>]=<<value>>

e.g
SELECT * FROM [cq:Page] AS page WHERE ISDESCENDANTNODE(page ,"/content") AND [jcr:content/test_node/test_property=test

http://<<AEM Host>>:<<AEM Port>>/crx/explorer/ui/search.jsp - Paste the query and click on Search Now.