For boys aged 12, you can consider choosing sports shorts, such as basketball shorts and football shorts. These shorts are usually breathable and cool to wear. When choosing shorts, it is recommended to choose the right size, not too tight or too loose. For underwear, you can choose comfortable and breathable styles suitable for sports, such as sports bra or boxer shorts, which can provide better comfort and support and avoid discomfort. In the choice of colors, you can choose brighter colors, such as blue and green, which can better echo the sunshine and beach atmosphere in Hainan.