"Is he younger?" Nikolas asked. He couldn't recall if Lucy had mentioned her brother the last time they had spoken. He didn't think so - or maybe she had, and he'd just forgotten. Either way, the way Lucy had described Grayson's amusement by Zonko's items made Nikolas assume a younger boy for some reason, and obviously one that had not yet begun his schooling at Hogwarts.
Clearly, the idea that Lucy's family wasn't of wizarding descent didn't even occur to him.
"My sister went through a phase about a year ago where all she wanted was things from Zonko's. And a pony."