My DS is 5 and my nephew is 9, they both love legos, kinex, magnetix (basically any building toy), star wars, spiderman and batman, so a 7yo boy should love any of those.
A 6 year girl is easy (and fun) to shop for. Maybe because i only have a boy. anything barbie, my little pony, dress up stuff, princess stuff, dolls or bears, care bear, doodle bear, jewelry, hair accessories, etc.