Lion Brand has a pattern for the scarf so I would check that first. I generally only crochet since my knitting skills are limited but unless you use sport weight working in the round would be (I think) too heavy for a child.

Here is a link that might be useful: Lion Brand - Harry Potter scarf

Thanks profsusan. I guess I have to use that pattern from Lion Brand. Just wanted both sides the same, so the pearl side with yarn addition wouldn't show.

I know this won't be the traditional HP scarf, but can't you just do a garter stitch for the whole thing? No border? that way both sides would look closer to the same. Or would your nephews know the difference and care -- I don't know. Look at some publicity shots for the movies to get a feel for where you want the stripes, and then just knit away! The stripes in the Lion Brand scarf don't look right to me but I've only seen one movie so I'm not an expert. :)

If you don't like knitting in the round, you can always knit it flat and then stitch the seams together. I don't think it would be too heavy, depending on yarn... the finished ones I've seen vary a lot in width so you can always make them a bit on the narrow side, too.

I'm including another link just FYI. When I googled for the scarf, I found tons of links and images, but it does look like most of them are knit in the round.

Just some thoughts. I'm strictly a novice so my expertise is limited! Whatever you do, have fun!

Here is a link that might be useful: another HP scarf

The alternative would be to knit two flat pieces and seam them up, but I think that is worse that knitting in the round.

The ones I have seen, they are not too thick when made in the round - the down side is that you have to use a lighter weight yarn than if you were knitting a single layer scarf, so it takes even longer.

I'm a big HP fan and I'd love one for myself, but I don't have the patience to actually knit one. All that mind-numbingly dull stockinette!

You are an amazing aunt if you make 3 of these.

Have you seen the book Charmed Knits? I might check it out of the library and show your nephews. You might be able to sell them on socks in their house colors, or a Hermione hat or Dobby socks or something that might be a bit more fun for you.

(They also have the scarf pattern - actually I think they may have both the stripe pattern from the first film and the current design)