All coaches and parents should always err on the side of caution when dealing with situations involving lightning and inclement weather.
Referees have been instructed to enforce the CSA Lightning Policy.

The safety of players, coaches, management, and spectators is the primary concern in any weather event that occurs during all matches sanctioned by Canada Soccer. By understanding and following the Lightning Policy, the safety of everyone shall be greatly increased. Ultimately, the referee has the final say over delaying or restarting a match due to weather. Waiting to stop play or not waiting to start play may result in a serious injury or loss of life. Referees are expected to act responsibly when dealing with such events during matches they are controlling.

If you can hear thunder, you can get hit by lightning. As soon as you hear thunder, quickly get to a safe location. More people are struck before and after a thunderstorm than during one. 

For the full PDF of the Canadian Soccer Association (CSA) Lightning Policy click here - Lightning Policy