On page to purchase TT, it is showing as $17.99 per return. In the past it allowed a number of returns. I do my kids and mothers, how do I find the multi file product

On the DISK version you can prepare 20 returns on one computer. 6 for those over $25,000 net income.

I already have an account and I have filed my wife and myself. I do not see how to add my daughter and son.

If you want to create additional returns in TurboTax Online go to the Tools link at the top of the screen and click Return Manager. Then you can click Create a new return. All the returns you create are stored in the Return Manager.