If there is no possibility that your child does not remember the password and assuming that you will lose all the data you have on your system, you must perform a Windows restoration with the files that you can download from the downloads section of this forum.
Tutorial: [Hi10 Air] [Tutorial] How to reinstall Windows 10 for Chuwi Hi10 Air
Windows: http://www.mediafire.com/folder/nxlndr1f48nyf/Hi10_Air