Moshe Rabeinu called those sons “youngsters” to imply their childlike and inadequate behavior. When the Pharaoh asked Moshe, “Who are they that shall go?” Moshe replied, “Our youths and our elders, our sons and our daughters.”
Moshe feared that those “youngsters” would spoil the sons and daughters who were instructed by the way of the Torah and Mitzvoth. He made a distinction between them by mentioning the elders, in hopes that the wise older men of the group would correct the youngsters’ bad behavior and make them repent for their evil deeds. Even if the elders were unsuccessful, at least the pure children would be separated and kept away from being influenced by their evil acts and attributes.
We must understand how important it is to create a holy atmosphere and pure love for Hashem in the youths of the flock that are the generation of the future. If a person does not plant the love of the Torah and devotion to Hashem in the hearts of his children, the young children may bind themselves with “youngsters” who misbehave and lead them down to rock bottom; this is what happened to Miriam. The work of the Beit Hamikdash was not honored and appreciated in her family’s home; she did not absorb holy feelings towards the saintly work of the Beit Hamikdash. Miriam socialized with evil persons who were able to drag her down to the furthest point from Hashem until she was converted. When she entered the holy temple, she scorned it and behaved in a disrespectful manner. Her parents did not plant the love and devotedness to the Torah, instead, they inserted a disregard for the work of Hashem.