Child policy (Different DNS) based on Mac address

Hi All,

I have a phone connected to a Unifi AP with an ERL Lite as router, with a DHCP server.

The DHCP issues dynamic addresses, also for my child's phone. The ERL Lite is connected to a single WAN and I get a fixed IP from the internet provider

I want to my child's device use OpenDNS as DNS server, and have all other devices use Google DNS.

How would I configure my firewall (or DHCP server) to make sure the device always uses OpenDNS?

Thanks,

Ro