So on the one hand he's saying this:
"Perplexed by that tweet. You said the Ickabog was for seven to nine year olds. The lower age limit for twitter is 13."
So he knows that children aged 13 are allowed onto the site and many will be following JKR.
But when it's pointed out that for younger children, their parents will be tweeting their artwork he says this:
"But it raises the question why Jo is talking about needing to protect children"
I'm sure he already knows this but Jo is talking about needing to protect children because:
- 13 year olds ARE children.
- Younger children still might have some access to the site, regardless of whether or not they should and responsible adults know this.
- By reporting the perverts responsible but refusing to otherwise engage with them, she's protecting everyone else from having to see the images (including the people in the images should they need to be protected) in the best way possible, regardless of how old they may be because it's not just children who don't want to see it (and that's exactly while the vile fuckers posting it are doing it, because they know that and do does he).