'Ere is an eye-dialect spelling of "here," representing dropped-H pronunciation in certain British English dialects (Cockney, West Country). Not concerning, just dialect vocabulary. If your kid uses it constantly, ask them where they first heard it, not to police their speech but to understand which online community they are in. Most slang of this kind moves through TikTok and group chats, so seeing it in your child's vocabulary just means they are plugged into normal teen internet culture.