Yarn weight question

[Tammyd]

I am using a pattern for a boy's sweater that calls for some pretty thin yarn, but my son wants thicker "camo" yarn. I cannot get the gauge even close with the recommended size 8 needles. Is it better to use smaller needles or make a smaller size? I am a new knitter and only know the basics.
Thanks.

[suzeeq]

Make the smaller size. One size down may not be enough, take your sts per inch with the yarn and size 8s times the finished measurement you want (should be about 2" more than his chest size, or a little over). Then see which size has that many sts in the chest, but do the lengths by the measurements given for sleeves, underarm to shoulder and underarm or shoulder to hem.