Has your child lost on time before?
Remember: "Feeling" low on time and losing on time are two different things. Many kids only get in time pressure when they realize they are losing, and they use all of their resources to try to salvage a losing position.
It's most important for the player to play a lot of good chess players in conditions where that player tries hard to win.
It is also important for the player to learn how to play weaker opponents but win consistently. This skill comes from experience, and it is the reason why the top half of a National tournament loses their rating points to the lower half.
If you are a Master playing against a bunch of 1600 players, you will occasionally lose games due to silly mistakes or time pressure if you are playing a fast time control. But every Master I know plays blitz, g/25, g/120, and basically every possible time control available.
Never hand-pick your opponents, be flexible when planning tournaments, and just be flexible.
And maybe avoid blitz and 1 minute chess (it depends on the kid, but when in doubt, avoid blitz and 1 minute chess).