Is there an easy way to get green card? My 18yr old son was actually born in usa.

Does your son have US Citizenship right now? If so he can sponsor his parents to move to the US with a green card.

Here is a link to USCIS (US Immigration) where it is explained in a bit more detail, you can download the forms off the website also.

Immigration through a Family Member (http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=0775667706f7d010VgnVCM10000048f3d6a1RCR D&vgnextchannel=4f719c7755cb9010VgnVCM10000045f3d6a1 RCRD)