Good observation. However, I don't agree, for the following reasons. Keep in mind that this is just how I think. On an objective level I agree with you: every pointless death is one too many.
The reason I think babies and young kids are more precious than adults -in terms of tragedy- is that they cannot influence their life yet to the point where what happens to them is a consquence of their own action.
For example, if I get mugged on the way home, it is not my fault. Please, I don't want to argue right and wrong here. But what happens, happens as a consequence of my choices and actions. I could have taken a different route if I thought it was dangerous. I could have learned MA enough to defend myself. I could have worn a bulletproof vest. ETc. No matter how or what, at least the outcome of the situation depended in part on the choices I made.
A baby or child or for that matter an unborn foetus cannot make all choices. the legal guardian in whatever format is making the choices for them. Whatever happens to them, they cannot influence the outcome, or not yet in any meaningful way.
They also cannot know the ways of the world yet. They have to be taught. Until they reach the point where they can physically and mentally make choices for themselves, someone else is trusted to do this and to help them get to the point where they can do so.
So I think the death of little kids and babies is more tragic because not only do they die, they die (usually) because someone else screwed up, or betrayed that trust. Adults can die because someone else screwed up as well, but they were in charge of all the decisions leading up to the untimely demise.
A baby dying in an overheated car because of parental neglect is worse than a teen getting hit by a train while trying to clear the intersection by zig zagging between the poles out of impatience.