These pictures are from almost 3 years ago when my son still thought it was fun to match his sister. I don't do much matchy matchy sewing anymore because he is rarely willing to match with her anymore. That said I think the biggest rule when doing matchy outfits for a boy and a girl is to make sure the fabric is boy fabric. Yes, I think a man can look great in a flowered shirt but good luck getting your average 5 year old boy into one. Plus, even when he was a baby it always bothered me when people asked it he was a girl.
My first offering is made from dragon fabric that I found at JoAnns. It was just quilters weight but I decided to go ahead and make him wild print shorts. Then I added dragon iron-ons to a ready to wear tee. The shorts pattern was Otto 3/07 design 22. He had several pairs of these and and it was my go to shorts pattern until he outgrew it.
Oliver and S one. That said I think a camp shirt and a jumper are a great way to have a son and daughter match without either one looking silly.