OQL is different from SQL in that it allows you to use the associations instead of joining tables 'ON'. This allows you to Join over the associations eg:
SELECT family.Name, family.ChildName, family.ChildAge FROM MyModule.Parent AS par INNER JOIN par/Parent_Child/MyModule.Child AS family
EDIT: I would also suggest you to always alias your results, it just makes it easier to understand and less likely to make a mistake.
For an example:
FROM MyModule.PARENT AS PARENT
INNER JOIN MyModule.CHILD AS CHILD
ON CHILD/MyModule.CHILD_PARENT/MyModule.PARENT/ID = PARENT/ID