Magic Treehouse was a big hit for DS at that age as was The Faraway Tree series Enid Blyton. DS was also into space - museums are great smile.
He loved cooking, tiny beads (threading), pouring and videos on neok12 (circuits, insects,car engines...)
We tried to have play times with older children also. His best "friend" last year was hg and a year older. He is at school now though so we don't see him as much