The Ukrainian Army knows where the troops in the Donbas are. Thus, the Ukrainian Army fires deliberately at civilians, which leads to the death of children as well.
Summary
As for the regular troops of the Russian Federation, they are not in Donbas. This is recognised by absolutely everyone, including on an international level. Therefore, what Zelenskyy said [at a press conference about the participation of the Russian army in the conflict in Donbas] is the purest delusion and lie.
Disproof
A recurring pro-Kremlin disinformation narrative about the war in Ukraine, claiming that Russia is not part of the conflict in Donbas, that Russia has nothing to do with the war in eastern Ukraine and that there is a “civil war” in Donbas.
There is ample irrefutable evidence of direct Russian military involvement in eastern Ukraine. The EU condemns the clear violation of Ukrainian sovereignty and territorial integrity by acts of aggression by the Russian armed forces since February 2014.
In 2015, Russian President Vladimir Putin admitted Russia's military presence in Ukraine.
Read similar cases claiming that there is no evidence of Russian presence in Ukraine, that Russian troops have never been in Donbas, that OSCE did not confirm Russian presence in Donbas.