Here is a free on-line pattern that I knit once that was very easy. It is almost all garter stitch, with a band of something else for interest, but not hard at all. It buttons like a cardigan but you do self buttonholes as you go. It is a pattern that can be worked in any yarn you want. It works for a boy or a girl. It has minimum finishing.
The name is Haiku, from Knitty.