In fact a little bit of rummaging and it turns out "jamp" is a scots word - used by RM Ballantyne and is shown in a ballad from 1860 ish called " Lamentation on the loss of the whittle"It was also used by Lewis Carroll in "sylvie and Bruno" around the 1890's i thinkIt appears to be of dundee/perthshire origin but i have seen it referred to as shetlandic in origin too.Isnt this a natural part of the development of language though? it might be "wrong" today but then it might be "right" tomorrow. Language is a living growing and changing beast. It doesnt stand still and it is not a respector of mums and dads, grandparents or anyone else. The scots language is a rich and resonant language in its own right - its apparently NOT simply a dialect of english , in fact a liguist friend of mine said Scots is related to english in the way portugese is related to spanish - of the same root but not the same language. If your child says "jamp" instead of jumped you maybe should celebrate their "scottishness" instead of crrecting them - although i can see that might not always be very popular