It's Burda magazine #136 from March, 2007. What a great source for children's patterns. I never throw those magazines away, and eventually you realize you have a fairly classic pattern for most children's garments, and quite a few adults as well.
I realized that most Hawaiian prints are very large-scale, and would overwhelm a small boy. Luckily, we have a great source for prints of all types here. The Cosmic Cow. It's a quilting shop, but a really great one. I was pleased to find just what I wanted.
I've made a lot of shirts, but never one this tiny, and it was fun.