Child Nameservers can be created from your Domain Panel.
1. Log in to your domain panel.
2. There is the option for Private Nameservers then you will get the option to create Child Nameservers.
3. There enter the Child Nameservers you want and the IP of the Server then save changes.
4. After creating the Child nameservers, need to update them in the domain panel.
5. After updating name servers it will take 5-6 hours to live your site.
6. Follow the same steps for creating the second Child Nameserver.