There was a whole "exposure" for what the show really was a few years back. In reality the kids have a trust fund set up for them by a uncle. All 8 have enough money set aside that their education is 100% paid for at a 4 year university. There was no number given, but they are taken care of.
The parents (Kate especially) whored the children out, they got free stuff all the time and peddled a sob-story that they didn't know how they would feed the kids and pay for school clothes, college, etc. In reality the kids had the trust fund, food was available all the time from local charities, and they had 40-50K in savings and several CDs that were given to them by family.
They went state to state in the beginning, going to churches, asking for money from the congregation. They charged the venue (which included churches) thousands of dollars for them to speak, this did not include the costs for flying there, their entourage, food, and hotel, which they made the venue pay for.
All the while they were also getting paid lucratively by TLC. The children never saw any of that money because of the contract that Kate and her agent had written.
If you watch the first couple seasons you will notice that Kates sister was on the show helping with the kids. She isn't on there anymore. She was offering her time for free but in season 3 TLC offered to pay her since she was on camera for some many hours and episode, Kate and her agent kicked her off the show and stopped all contact with her and did not allow the kids to see her either.
I stopped watching after season 2. It just got frustrating and I could not watch Jon get the life slowly sucked out of him by his overbearing wife.
This show will die off in a couple years, and when the two oldest daughters are 18 expect to see a law suit against Kate and Jon (assuming he is still alive) by the eldest daughters with the 6pack as co-plaintiffs to take whatever money and property they have left as back pay from the show that they did and and probably will never see.