The first time Moshe announced Hashem's promise to bring the Jews out of Egypt, everyone believed him and knelt before him in thanks.
But when they saw that the promise wasn't fulfilled immediately, they became disillusioned. Their hard work made it very difficult for them to listen to Moshe.
Then Moses brought the message of redemption to Pharaoh. After ten plagues, Pharaoh let the Jewish people go. But even after leaving Egypt, the Jews were afraid. Some were so terrified of the Egyptians who were pursuing them that they even considered returning to Egypt and becoming slaves again! Only after the miracle of the parting of the Sea of Reeds did they feel free and safe.
However, the Jewish children did not act this way. They always maintained their faith and trust in God, because Hashem protected them from the decrees of the Egyptians.
In many ways, the redemption of Messiah will resemble that of Egypt, and children will have a significant part in it.
We all want the Messiah to come, but adults are busy with work and paying bills. Children don't have these worries and responsibilities. They can focus on what they truly want, which is the Messiah.
The dictionary defines "want" as also meaning a lack or a need. Jewish children feel that something is missing because Messiah has not yet arrived.
But we won't have to wait much longer, because Messiah will come very soon. When he arrives, just as happened at the Sea of Reeds, the children will recognize him first.
Adapted from Please tel me what the Rebbe says.