There are young people now leaving school in the temporarily occupied territories of Crimea and Donetsk and Luhansk oblasts who have not spent a single day studying under the Ukrainian curriculum. They were only five years old in 2014, when these lands were occupied.
If / when Ukraine retakes those regions, it would be a grave mistake to “re-educate” those Ukrainian kids raised as Russians. If their entire life’s worldview is turned upside down and inside out by what they will perceive as enemy propaganda, they would become a very dangerous Russian 5th column in Ukraine.
Instead, they should be shipped off to Russia - or allowed to remain in their country but as Russian citizens - and offered automatic, immediate and full Ukrainian citizenship if they decide to apply for one. But forcing them back into a society they’ve never known is going to be traumatic for them.
Many German kids at the end of WW2 who grew up knowing nothing but Nazism experienced something similar and ended up scarred for life.