Just got the US-citizenship last month and I'm currently filling a I-130 to bring my son and his wife from Belgium to the USA. Is it true that the processing time is about 7-8 years ? It is that long (even from Europe) ? ?

Yes that is true this case is considered to be third level of preference, there are a limited number of visas available per year, makes no difference what part of the world.

http://www.uscis.gov/lpBin/lpext.dll/inser...m#slb-act203a2b
http://www.uscis.gov/graphics/services/imm_visas.htm