The Midrash tells us that at the moment when the Jewish People were in front of Mount Sinai to receive the Torah, God asked them for a guarantor to ensure that they would fulfill it and take care of it in order to deliver it.
The people first said, «Our patriarchs are guarantors for us,» but God did not accept. Then they said, «Our prophets are guarantors for us,» but God did not accept. Only when they said, «Our sons are guarantors for us,» did God accept.
This teaches us something very basic and fundamental: it is in children that we find the purity and simplicity necessary to ensure that adults connect with God. That is why they are the only guarantor that God accepted.