I must admit I don't feed during the summer mainly because I think most baby birds naturally are fed insects (because seeds are a late summer and beyond thing) and this must be what their little bodies have evolved to require. I am planting lots of things to boost insect numbers though....
I'm sure probably adult birds are bright enough to work out what their babies should be eating - hopefully they have more sense than humans!! but just incase they're not I'll try to boost the natural bird table.......