That's wonderful that your grandson has learned so much and actually finished some dishcloths. My children liked learning and that was the end of it.
I'd try the library or a bookstore first to see if the patterns look do-able to you. There are some books on Amazon that look like possibilities, too. I'm onlly familiar with "One Skein Wonders" but you might look these up and see what you think. Sometimes the reviews both positive and negative are helpful.