I'm not sure if I'm naming the right one..? "vlan?" (I know or assume some routers "do" have this feature) But with wifi easily hackable WEP and some parts or all parts of wpa? Why don't router ...

If you need to have devices on your LAN reach the IoT devices, create a new firewall rule allowing "Match State Established" and "Match State Related" from your LAN to the IoT VLAN.