I recently made a fleece hoodie for my son for Playcentre. I chose a fleece with rockets and planets as he has an interest in all things space.
I used the All the Rage Raglans pattern with optional hoodie from CarlaC, the ScientificSeamstress.
As I was using fleece rather than jersey, I did as recommended, and went up one size from his usual to a 5.
As always, the instructions were well written and left no room for confusion. The only change I made was to top stitch the raglan seams, and the hood seam.
Next time I plan to add extra seam allowance to the raglan seams so the topstitching works a bit better.
I was a little worried when it was finished, as it looked really long and narrow, but actually when he wears it, and lifts his hands up high it still covers his tummy - so we are calling that a design feature!
T is quite slim, so would suggest maybe going up a couple of sizes for the extra width through the body if this is not the case for your child.