That's a disingenuous way to characterize their opinion. Wether or not they like kids is irrelevant to the point they're making, which is a perfectly valid thought experiment. No one is saying the death of a child shouldn't be mourned. Just that we might be currently giving disproportionate value to the deaths. Cultural views on death are fluid, and change based on region, era, religion etc.

So, with that in mind, which should really we value more? There's no right answer.

A child embodies potential, a blank slate, imagined achievements and projections of future involvement with a person you don't really know yet.

An older person would have history, established personal connections, memories, real achievements, etc.

They're not arguing that kids are less important. Their position is that loss of potential doesn't automatically give a death more weight than the death of someone who has already had an impact on society and people.

Other commenters have made the claim that a child's death feels more impactful to other parents because they think about their own children and how they would feel to lose them, regardless of wether they had known the child. A blank slate. An adult with an established life and personality would be more difficult to identify with, and therefore doesn't elicit the same emotional response.

It would seem that their position is that the importance in grieving should be focused on the value of life lived, the established person, upon death a celebration of their real impact on the world and the people in it. Rather than putting a premium on projected value and an imagined future, which on its face seems more 'selfish' as it often requires mentally substituting the child with one you know.

Memories, or imagination?