We are on a holiday in Finland now, so I have been making Summer clothes for the boys lately. It can get very warm in Finland over Summer although last few weeks have been quite cool.
Since the little one is only 10 months old, I have made light long trousers for him that are not too hot to wear on hot Summer days but still protect his sensitive skin from the sun. I used thin cotton to make comfortable harem pants with a pocket on the side. The front and back are of different fabrics. In front I used old retro curtain, and backside is recycled spotty cotton. The pocket is also black and white dotted cotton. Comfy and cool!