This is confusing. The Outdoor Annual from TPWD lays out the rules for Youth Hunting. Permit, Parent, under 15.

The Texas Youth Hunt program has a bunch of rules that include "registering for an official Youth Hunt".
https://www.texas-wildlife.org/tyhp/youth-hunters/

Can I take the boy out Sunday, or do I need to register w/ the Official Youth Hunt program first?

That's if you want to join that program. Your kid does not have to join that program to participate in youth season.

Thanks Guy,
Thought I was reading it correctly, but the Youth Hunt Program thing sort of threw me. Don't want the Warden telling me I'm misinformed and handing me a hefty ticket!

tyhp is specifically for youth to hunt and is family oriented. you have a huntmaster that sets the hunt up and finds guides to take all the children and parents out. the parents are in charge of the ammo and kid is in charge of the gun. It is a great program that i would recommend you going ahead and signing your kid up for. I greew up in the program and met my wife while we were 15 we are now guides and she is a huntmaster.