Hi,
I have never filed for child support ever. My kids are now 8 and things are getting harder.
If I were to file now, would I get arrears or would I just get from the file date forward?

No you can not collect anything prior to the date you file.

That depends on where you are. ANY question on law needs to include your general locale as laws vary by area.

But generally you only get from when you first file. There are no arrears if he was never ordered to pay anything. But some states do allow an award to be retroactive.