The school was located on a former military base. 10 years ago, that location was a legit military target. Nobody bothered to update the satellite imagery from 2013 when feeding it into whatever LLM was assisting in targeting. It saw an airstrip and missile base. The human reviewing the targeting saw an airstrip and missile base. When you go to take out a military target, you don't send one missile. You send a missile or two in first, and then another couple in a few minutes later.
Hanlon's Razor very much applies here. There's no need to posit that the children were IRGC members or that the attack was deliberate or even that the children were the targets. There's a very obvious explanation, which is that nobody bothered to check the date and assumed that if it was military base in 2013 it was still a military base today.