OppoSuits Sizing Chart. Boys’ – Suits. US / UK / AU10Y – 12Y 14Y – 16Y. Teen Boys’ Onesies (10 – 16 YEARS). EU92/98 – 98/104 110/116 – 122/128. US / UK / AU2Y – 4Y 6Y – 8Y. Boys’ Onesies (2 – 8 YEARS).