I know the online version charges $36.99 to prepare and e-file each state, which is a bit steep. Sounds like you're using the desktop version of TT, not the online version.
Were you expecting to prepare and e-file your state return, then use the software again to e-file you kid's return? I'm pretty sure TT would block that because what would stop someone from using the desktop version to file many returns? I'm pretty sure TT supports one filing per purchase. I guess that's one advantage of the desktop version is you seem to be able to prepare and print multiple returns.
I should have noted we are using the Desk Top/CD version. They do allow I think up to 5 returns to be filed with the feds, can't be for profit filing however, think its meant for someone like myself to help the kids out etc.
When using the desk top version they give two options for state, you can charge $20 to your CC or its something like $35 and they will take that from your return.
I keep saying next year I'm going to try other software, will see what 2017 brings! My kids is so simple they could use just about anything, by rights they should do a few years by hand to get a better understanding of where the numbers come from!
Maybe Trump will get his hands on the tax filing and get it down to one page!