I'm not sure about once upon a time, but I'll give you some correct examples:
an bata beag an feadóg bheag na bataí beaga na feadóga beaga
ar an mbata beag ar an bhfeadóg bheag ar na bataí beaga ar na feadóga beaga
cara an bhata bhig cara na feadóige bige cara na mbataí beaga (NB: Strong genitive plural) cara na bhfeadóg beag (NB: Weak genitive plural)
Looking at the last sentence immediately above, I don't think anyone says "cara na bhfeadóg mbeag" anymore, but I do have one or two old books that have that form.
On another note, whereas you'd normally see "ar mhadra beag", you'll also see "ar mhadra bheag".
Fáilte Roimh Cheartúcháin Ceartaigh rud ar bith atá mícheart -- úsáid phrásaí go háirithe.