Irish law is very specific. No Irish children can be adopted by non Irish citizens. There are no exceptions.
Roberts is not an Irish citizen and he has two Irish kids here in America.
The records are sealed but the theory is that Roberts got two Irish women who had given birth illegitimately to leave Ireland with the kids and travel to South America, and then the children were adopted by Roberts.
Check this out:
http://underneaththeirrobes.blogs.com/main/2005/08/the_roberts_ado.html