From the Introduction:
Dr. Wanda Wilson couldn't understand it. All of the calculations were correct. She'd sent objects back in time, that was for sure. Not smart phones or radios, of course, but spoons and knives, sure! She'd sent animals back in time, but why couldn't she send people? People didn't cause paradox events, so they should be able to be sent, but each time, the team just sat in the Wilson Transform Box and nothing happened. It just didn't make sense.
Then, one night in the lab, Wanda's daughter Erika began walking around in the lab. She was supposed to be doing her homework, of course, but that was boring, and she began wandering around the lab. Dr. Wilson had decided to try sending a spoon back in time to witness the signing of the Declaration of Independence, something that had worked before. She looked on with horror as she saw young Erika in the Wilson Transform Box. Dr. Wilson's fear was not because Erika would be hurt, but that Erika would ruin the experiment. People couldn't be sent back! Nothing would happen!
To Wanda's amazement, she was wrong. Erika disappeared along with the spoon! Would Wanda 's daughter return in the 24 hours allotted? Wanda hoped so. 24 hours later, Erika and the spoon re-appeared in the Box. Erika described what she had seen. She'd seen Ben Franklin just like in school! She'd seen John Hancock sign the document! The details were too detailed, too amazing to be wrong!
Wanda finally figured it out. Adults, with their knowledge of modern events, would cause the same paradox events that would be caused by advanced technology, but kids would be unobtrusive enough to prevent the paradox. With the help of Wanda and scientists like her, historians began planning to getting information they needed with Kids in Time.