How do I help my young fencer build the stamina and mental toughness to last a whole tournament day?
Build both slowly, over a season, mostly through more experience of long bouts and a few habits your fencer practices until they are automatic. Fading late in the day is normal for a pre-teen, and it is usually as much mental fatigue as tired legs. Tournament days are long: pools, then waiting, then direct elimination. The jump between age groups is real too. Under USA Fencing rules, Y10 elimination bouts go to 10 touches over two three-minute periods, while Y12 bouts go to 15 touches over three periods, so the first season in an older group asks for a much bigger gas tank.
For stamina, the best training is fencing itself. Ask the coach for more full-length bouts in practice, to 15 with the score kept, and some bouts at the end of a session when your fencer is already tired, because that is exactly the feeling of a quarterfinal at four in the afternoon. Other active play builds the base, and sleep matters more than any drill: sleep medicine guidelines say children 6 to 12 need 9 to 12 hours a night, and teens 8 to 10. At tournaments, teach your fencer to stay warm and moving during long waits, because a fencer who sits cold for an hour often starts the next bout flat.
Mental toughness is a set of skills, not a personality trait. The most useful is a reset routine between touches: walk back to the line, look at the tip, one slow breath, one cue word such as "feet" or "patience". Practiced in every club bout, it becomes the thing they do when a lead slips. For the one-minute break and the waits between bouts, teach box breathing: in for four counts, hold four, out four, hold four, a few rounds. After each event, have your fencer write two lines in a notebook: one thing that worked and one thing to try next time.
How you talk about fencing over months shapes this more than any single conversation. Praise effort and specific choices, like a good parry or staying calm after two quick touches, rather than results or talent, and keep your tone the same after wins and losses. Let your fencer set their own goals with the coach, and track progress across a season instead of judging one event. Fun keeps kids in the sport long enough for toughness to grow. If they do not want to work on this yet, let it wait. For the hard day itself, see our answer on kids who fall apart at tournaments.