Try cleaning out the charging port on his iPad. Use a soft, clean, toothbrush, and give it a good brushing out. If there is any lint or debris in there, the charger won't make the connection, so it won't charge. Be sure you are using at least a 10w charger, and make sure that it, and the wall socket it it plugged into is working by hooking it up to another device (like your iPhone). Once you have verified the charger/wall socket is working, and once you have cleaned out the port on the iPad, plug the charger in again and give it 30 minutes or so.
After 30-60 minutes, see if it is charging. If it is, then you should be good to go once it is charged up.
If you are still having issues after it is charged, reset the device: Hold down the Home and Power buttons at the same time and continue to hold them both down until the Apple appears (up to 30 seconds). Once the reset completes successfully, the Slide to Unlock screen will display.
Best of luck,
GB