Thanks for reaching out — it’s great that you want to support your son’s interest. That said, downloading Null’s Brawl on an iOS device isn’t as straightforward as it might seem. Null’s Brawl is an unofficial version of Brawl Stars, run on private servers created by fans. Because it’s not an official release, Apple doesn’t allow it in the App Store due to strict policies on unofficial and modified apps.
Still, if you're set on trying it, there is a workaround. You can find detailed instructions for downloading and installing Null’s Brawl on iOS devices at this link: https://nullsbrawlpro.com/