I'm so deeply sorry to hear that, Universalsnail. It's a horrendous betrayal and a crime and it makes me so angry to hear about it. I hope that you have had support in coming to terms with it.
The issue here is not that anyone expects their children are at risk from this illustrator. That would, as you say, be absurd.
The issue is that there are groups of people who are invested in eroding, undermining and chipping away at societal boundaries. They may also be victims themselves, sometimes they may not be fully aware of the implications of what they are involved in excusing. They may genuinely think that they are just promoting tolerance and acceptance of 'varied' sexualities, or that society just doesn't understand their intentions.
Predators connect with each other, signal to each other and are collectively involved in trying to undermine societal boundaries and barriers. This is fairly uncontroversial. Look into PIE or NAMBLA.
Teaching children about the existence of gay people is fine, and has been done many times before in other books with no issues.
Teaching very young children about the history of LGBT activism is, I would say, too advanced, in the way that we don't teach four year olds about feminism or civil rights - it's just far too advanced for them to grasp. All teaching should be age appropriate, and trauma informed. Slightly older children can learn about activism and politics, perhaps upper primary age, although to be honest, I still think this is quite young to be learning about, say, the history of legislative evolution in regards to sexuality. Sexuality and politics is just not on the radar of pre pubescent children. They can't grasp sexuality or sex drive. Love, yes. Families, yes. Sex? It's alien to them, or should be.
Teaching people about BDSM, or fetish, or kink, or 'pansexuality', or 'Lolita', or MAPS, is another matter entirely. That's crossed the line very clearly into very, very dodgy territory.
When we get to the point where a picture book for four year olds with pictures of old men in bondage gear is chosen as book of the year, wins awards, and is lauded and read on TV?
We're in serious shit. As a society, we have been groomed. Our boundaries are shot to pieces.