The 1st two links I gave you were for the BSS and BSS Summer Edition, and both are available and have numbers on the top. So if you went that way, one would get a solid orange comb with shiny cover plates, and the other would get a translucent yellow comb with coverplates that have a matted finish. But again, there's the cost. That would be 60 dollars each for children, and children have a notoriously bad track record on "dropping things" and "dropping things in the toilet." The other danger is that the translucent comb would stick out as "objectively cooler" and then you're in a "but I want /that/ one" situation that you could avoid if you could just get them both their favorite color like you want.
2 cents on the numbers: I think it does help for learning, but it depends on what they want to do. If they're going to sit down with tabs, the numbers are definitely helpful. I'm not sure about necessary, but helpful. If they're going to just improvise whatever they want on it (which is more along the lines of what I imagine kids doing), the numbers probably don't matter at all.
The other alternative that comes to mind is this: if they are trying to play tabs but are having a hard time finding the right holes, you could go to a craft store and see if they have tiny number stickers. Something really small, place them far back enough that it'll be out of the way of their mouths (they'll still be able to follow from there to the holes with their fingers easily enough), and a piece of scotch tape straight across over that will probably make it so the won't rub them off very fast. Then you can explain that those are like training wheels to help them learn, and they can come off when they're no longer needed. And that way it can be kind of like a goal for them to be able to identify which hole is which on sight without needing to double check a number. They'll want to outgrow their "training wheels"
I have absolutely no clue how practical any of that really is, though. Maybe even with the tape over them, one sweaty song is all it'll take to kill the numbers. No idea, just thinking out loud. And again, it would only be necessary to even think about if they were expressing frustration finding the right holes by counting them each time.
By the way, when I was looking through amazon for ya I saw the turboharps and took a look. The first review just happened to address the very issue of durability. The review stated that the harps easily come apart if dropped onto the floor, but they also snap back together very easily with no lasting damage. I'll link you to the review, I'm not sure if it's the same model of turboharp you were looking at, but you can have a look:
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