Short answer: yes, a little. Watch any big fencing tournament and you'll notice something odd. A much larger share of top fencers are left-handed than you'd expect from the general population, where roughly one in ten people are lefties. On the elite podium, that ratio jumps way up. So there's something real going on here.
It mostly comes down to practice, or the lack of it. Most fencers are right-handed, so most bouts a right-hander fights are against other right-handers. They get very comfortable with that mirror. Then a lefty shows up, and suddenly the angles, the blade lines, and the target all sit on the wrong side. The righty rarely trains against that.
Meanwhile the lefty fights right-handers constantly, so facing a righty feels totally normal. That's the whole trick: it's a familiarity gap, not magic.
At the very top, the edge shrinks. Elite coaches drill left-handed opponents on purpose, and the best fencers have simply seen enough lefties to stop being surprised. The advantage is biggest at the beginner and club level, where nobody's had that specific practice yet.
No. Don't steer a kid toward one hand for a sport advantage. Let them fence with whatever hand feels natural, and enjoy the quirk for what it is. Find a spot to start at our clubs directory and let your fencer discover which side they land on.