But if Massachusetts makes it legal to beat your kids in Massachusetts, and a parent flies their kid to Boston to beat them, then comes back to Texas and doesn't beat them, can Texas do anything about it? The Trump supreme court may say Texas can indeed stop it, but they didn't like the way that the abortion law was to be enforced, so it's not certain if this will be upheld or implemented on a national level. A national ban would be difficult because licensing doctors is a states' rights issue for the most part. It'd have to be a virtual ban using federal funding, similar to how any state could lower its drinking age to 18, but then the feds would cut their highway funding.
What if parents take their kids down to Mexico to get hormones from a quack? Dr Gallagher already has some office in Mexico; she could easily set up a clinic in Juarez or Nuevo Laredo. I'm not exactly sure what the rules are with doctors doing trans stuff to kids in Mexico, but I do know that Mexico has some of the strictest firearms laws in the world. There are only two licensed gun shops in the country, so the rule of law is definitely in effect south of the border...
This could end up being like bans on female genital mutilation in Europe just driving fundamentalist Muslim parents to take their kids to the Middle East and North Africa. It'd actually be great if they stayed there, but instead they fly right back to Stockholm and Berlin.