5-4-3-2-1 is a grounding technique for anxiety: name 5 things you see, 4 you can touch, 3 you hear, 2 you smell, 1 you taste. Often mentioned by therapists and on mental-health TikTok. Not concerning, actually useful. 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.