"I want to say this once again to Russian mothers, especially mothers of conscripts. Do not send your children to war in a foreign country," Zelensky said in a video address released on Telegram.
"Check where your son is. And if you have the slightest suspicion that your son could be sent to war against Ukraine, act immediately" to prevent him being killed or captured, he said.
"Ukraine never wanted this terrible war. And Ukraine does not want it. But it will defend itself as much as necessary," he added.
On Wednesday, Russia for the first time acknowledged the presence of conscripts in Ukraine and announced that a number of them had been taken prisoner.
Moscow had previously claimed that only professional soldiers were fighting there.
The announcement came as posts from mothers without news of their sons sent to Ukraine multiplied on social networks.
Kyiv last week invited mothers of Russian soldiers captured on its territory to come and pick their children up.
The Ukrainian defense ministry published phone numbers and an email through which they could obtain information about them.
Kyiv claims to have taken dozens of prisoners since the start of the Russian attack.
During the conflict between Moscow and Chechen separatists in the 1990s and 2000s, many young Russian conscripts were sent to the front, and some were taken prisoner.
In a movement that fueled anti-war protests in Russia at the time, women mobilized to try and bring their sons back alive or bring their bodies back -- even going to Chechnya themselves.