Unsolicited critique is almost always unwelcome critique, in my experience. Especially where someone else's 7 year old is concerned.
The communicator does have responsibility on how their message comes across, thought not all of it. It’s on the receiver to also make an effort to understand what was meant and not take unnecessary offence. The comment reads pretty much neutral, apart from a post scriptum which is explicitly about the author’s preference. It’s up to you to inject the writer’s feelings as either “this code sucks, here’s how you do it” or “congratulations on making something cool, here are a few suggestions”.
My experience is that life is much better if you take the latter approach. Default to empathy.
Consider listening to “This is Water” from David From Wallace.