I have a lexibook junior tablet I purchased for my son it will no longer turn on nor charge. Don't know what I should do

Hold the volume UP botton down when it is OFF, then while holding that button down press and hold the power on button and keep both pressed for about 10 seconds. Then release.

try to look on youtube on this should be easy to set up , just goto setting and internet options etc ,

Your tablet is stuck in demo mode, to reset the demo mode shut off the tablet, keep pressed at the same time power+volume up buttons, the tablet will boot in recovery move, the last selection of the menu is the demo mode feature 0n/off

Is the green charging light displaying on the side of the tablet and/or does the screen indicate that it's taking a charge?

When you hold down the power button for 30 seconds or more, does the screen indicate anything? Charging? Battery low? Charged?

If it's new (and your son doesn't have any/much personal files on the device it's probably less headache to just return it to the store and get a replacement.

Hello,
I am very familiar with this problem with the 2nd gens and it is almost always a sure sign that the tablet is not getting enough power to charge up and will not boot. Sometimes this can happen from the tablet not getting used for a while and getting completely drained. The other possibilities are A) the USB charging port is becoming worn out and won't charge or B) the battery is no longer holding a charge, much like a car battery in the winter. Get an original Nexus 7 wall charger and leave it charging through the wall outlet and not a computer, this has more power. If the light is blinking, it makes me think the USB is not the issue, so chances are after an hour or two it will have some life again.

take the tablet to a store that sells charger , ask if you can test it before you buy it

Sorry I never saw this before, the best thing to do is to go back to the shop you purchased them from. If you bought them from a second hand source then the batteries are probably finished, they only last a year or so. You can buy replacements via eBay and when you get them, there are instructions in the following link to walk you through how to replace them.

https://de.ifixit.com/Anleitung/Lexibook+Junior+Tablet+Battery+Replacement/69214