How to write a kid character in apocalyps?

Hihi! So for context; I’m writing a story about a zombie apocalypse. In the book I have a kid character who is hard of hearing with hearing aids. But the thing I’m wondering about is, how old should I make her? Because she’s still young, has to be carried around sometimes because little legs and not as fast, but she’s mature enough to understand everything that’s going on.

I work with kids myself so I was thinking she should be 6/8 years old? But then I was wondering if 6 might be a little young but 8 is a little too old… I’d like your advice on how old she should be and why!

EDIT: I just want to say thank you to everyone who game me adice, especially to spare-chemical-348 for giving me some advice about her hearing aids since I mentioned. I'm going to just write her, I think I'll make her 6, but almost 7 if that makes sense. Rn I'm just going to think about her character a little more and how I have to dress her in a zombie apocalypse, just like the fellow main characters. BUT THANK YOU GUYS!! <33