Is he old enough to go as an au pair? Lots of families accept male au pairs, but there might be a lower age limit.
The Institut Catholique or the Alliance Francaise would be good reputable language colleges in Paris and provide recognised certification in French. Like TEFL there are lots of places that someone can study, but some are good and some not so good.
I'm not so sure of the AF but the IC also provide 'options' which are specialisations in French culture, e.g. art, music, history etc. Depending on how many hours he's planning on studying they might be useful.
If you contact the AF in Ireland they might have more details for you, or you can contact the IC here - [broken link removed]
Some schools in Ireland provide for foreign students to come and spend a year while improving their English - one that I know of is Colaiste Criost Ri in Cork, and also the secondary school in Crosshaven outside Cork city (not sure what it's called) - quite possibly they might have reciprocal arrangements with foreign schools, or they might be able to point you in the right direction.
Hope your son has a great time!