parents: this form (web application actually) is free to the kids.
it runs locally on your PC and there is no server backend (no storing anything). no server activity is done except to load the page into the browser. the browser does all the work because it is pure Dynamic HTML.
If this form is not from Jesusnjim.com then it wasn't by Jim Michaels. to verify, right click on the page and "View Source", scroll down to the bottom and check to see that <form action="kids-see-how-old-you-are-today.html" on the line below this. if it does not, then it's not a safe form and someone copied it and ruined it. DTime.js is a commercial library I wrote and you do not need to worry about the cost for this web page.
in order to do the subtractions on this page, I could optionally to subtract take the difference in time from Jesus' Birthday to get the proper time difference.
if you want to update the date, add spaces somewhere in the date like the end, middle, or beginning of the Birthday box.