Poaching Clients. Is It Illegal?

I’ve looked around for info on this but it seems a little case by case. I tutor kids for a company and want to quit. The owners are greedy and overwork all of us. I still want to continue working with my favorite kids. I already have all of their phone numbers in my own personal phone and want to reach out to them to see if they’d still wanna see me if i’m not working at my company.

Would this be illegal? Don’t want to get into any trouble here. I read some stuff that it would only be illegal if you’re getting their info from the companies internal database.

edit: I live in Colorado.