I am a father of 5. I have 4 girls & 1 boy. 11, 9, 7, 5, & 6mos.
I would be a basket case & extremely emotionally fucked up to be in your postion & I pray for your son.
I don't know what kind of tumor your son has, if it is a cancer type or not, but maybe this group can provide you with resources as well as financial assistance.
http://www.cancercare.org/get_help/assistance/index.php
I know medical treatment for terminal diseases is very expensive. My father suffered from colon cancer for 9 years until it killed him & the expenses nearly bankrupt him & his spouse, so I wish you the best in getting the help you need, but keep in mind that no hospital will deny your son treatment, worst case scenario should be that your son gets treated, survives, lives a long, healthy, prosperous life, & you can make payments on the bill.
I wish you, your son, & family the best of luck.