Teenage underwear is a category that gets treated as an afterthought by most of the market, which is a mistake. Teenagers are hard on their gear, they're going through rapid physical changes that affect fit and comfort, and they're at an age where being comfortable in what they wear actually matters to how they carry themselves. The practical guide to teenage underwear starts with the same principles as adult underwear: quality fabric, correct fit, and construction that handles real daily use.
What I think parents should prioritise when buying teenage underwear is quality over quantity. A smaller number of quality pairs that hold up to the washing machine and the demands of an active teenager is better than a large pack of cheap gear that falls apart in 6 weeks. The cost-per-wear calculation that applies to adult underwear applies here too. Quality teenage underwear that lasts a year is cheaper than cheap gear replaced 3 times in the same period.
For teenagers picking their own teenage underwear, the main consideration is comfort during sport and school days. Most young blokes do sport, PE class, and a full day of movement, then come home and do it again. Underwear that handles all of that without becoming uncomfortable by the afternoon is the right call. The trunk cut tends to work well for most teenage blokes for the same reasons it works well for adult men: support and coverage without excess fabric.
From my experience helping parents navigate this for their kids, the conversation is simpler than most expect. Buy quality. Get the right cut for the activity level. Replace when worn out rather than waiting for them to fall apart entirely. Barramundies makes teenage underwear options that hold up to the demands of an active younger bloke without the premium pricing of some adult ranges. The same principles that make their adult range good apply here. Good fabric, honest construction, genuine durability.