When you breed 2 tagged pets of the same theme you get a pure bred offspring.

But, if you breed 2 PB offspring together will their babies also be a PB offspring?

And are PB offspring as valuable, or less valuable, as their parents?

Offspring of two PB offspring of the same type would still be considered PB offspring.

If you're buying or selling PB offspring that are not immediate offspring of the tagged pets, you can double check that the offspring is, in fact, PB by tracking back through the lineage - this can get complicated if the offspring is multiple generations after the original tagged pets.

Generally, PB offspring are less valuable than the actual tagged pets. That said, offspring could be more expensive than a tagged if it had been bred to the point where it had a large number of carried and/or visible traits, etc.

Edited: To, hopefully, make more sense.