Hi Paul.
I have of course guessed your answer, as I suggested at the start of my response. I haven't read any of the books which claim that children don't or can't remember past lives. Perhaps you could recommend some. So I wonder if their argument is something along the lines of: reincarnation, therefore past-life memories are impossible in principle, so that arguments have to be found to dismiss any evidence which appears to suggest the contrary. Do they actually objectively assess the evidence, and offer credible alternative scientific explanations?
If you're interested, I've written about Stevenson's work in these articles – the first and the third are the most relevant:
Reincarnation — Memories of Past Lives | by Graham Pemberton | Medium
Reincarnation and Birthmarks. In a previous article I discussed the… | by Graham Pemberton | Medium
Reincarnation and Birthmarks — More Thoughts | by Graham Pemberton | Medium