Kid’s writing is awesome. It’s creative, it’s unexpected, it shows me what excites them, and sometimes it’s a cryptic way to ask for advice. It’s precious. And it’s something else – easy to criticise. So my thinking here is: do not criticise. At all.
Point out all the good stuff.
Point out good description. Congratulate good ideas. Explain how you understand the character because of what they have told the reader about the person. Point out the conflict and the dilemma and wonder about what would happen next. If there are two words sitting nicely together then point them out, how they sound so good. If something is done differently say how original it is. Say what you’d like to know more about.
When you’ve pointed out all the good stuff you can see you can ask what got them inspired to write the piece, what they think about it, if they think they’ll write some more. Offer to read more.
There will be plenty of people in that kid’s life who will see their writing and focus on the spelling and the grammar and the bit that doesn’t make sense. They will chip away at the joy of creating an imagined world. Please don’t worry about the stuff they got wrong. The kid will go back at some stage and think oh yeah, I spelled that wrong and missed a comma. There will be very few people who celebrate everything that went well for a fledgling writer.