Please check this page.

Yes, I understand that. But I don’t have passes for my kids. How do I add them to mine?

Did you indicate 2 children when buying the pass? If so, I don't know how this would work. If not, then you'll need to change your pass.

Note that on some railways-but I cannot list these here, these 2 kids are then only entitled to 1 seat-they have to share. I did not invent this, those are the rules from the state-burocratic railways also watching their incomes.

I’ve figured out that I need to add the kids at the time of pass purchase. Now that it’s too late and I already bought my pass, I need to exchange it for a new one and add the kids. Any ideas on how to exchange the pass?

Exchange conditions depend on what you chose at pass purchase. To do an exchange, check this page.

Please note that Kids pay the same reservation fees as adults means if you pay 10€ for a seat (e.g. A french domestic TGV) you have to pay the same for your Kids (depending on their age its sometimes cheaper to use standard fares. For example in germany Kids under 15 travel for free with a paying adult) the problem here is that each country(rail company) have a own age limit :/ 

Do you mean if I’m only traveling in Germany, I don’t need to buy a child pass? I’ve been staring at Eurail all day and I can’t find anywhere to add my children once I select German Rail...

Possibly. It doesn't say it explicitly but indeed the boxes to add children are not there.

Thank you so much. I thought for sure I screwed up somewhere. I’m glad to have another pair of eyes looking at it for me. Thank you!