By the way, the derivation from Celtic numbers is very speculative. No numbers in any Celtic language sound like eeny meeny miny mo, for example, though the number one sounds a bit like eeny, as it does in Spanish (Uno) and many other indo-European languages. There was a time when proving a "Celtic" heritage for any piece of folklore was fashionable, because (in England at least) it suggested that the the folklore in question was very old--a survival of before the Saxon conquest of Britain. Since the first folklorists were antiquarians, they were always claiming everything they recorded was an ancient fertility rite of Celtic or pre-Celtic times. People have even claimed that "eeny meeny miny moe" became a counting out rhyme when it was used by druids to select among prisoners for one to be sacrificed!
That said, there are various weird-sounding counting systems in England, for use both in counting-out among children, and counting sheep among shepherds. Some of them do have clear Celtic parallels, while for others scholars jump through hoops to try to fit them into a Celtic mold.