No difference. Year of manufacture, colour or some plastic part that is 1 millimetre shorter. This automatically changes the model designation because the plastic part no longer fits on the 970.
Unfortunately, I couldn't find this information anywhere on the manufacturer's website or on the internet in general.
It is best to contact the customer service directly :)
Nope.
http://www.lenco.com/p/scr-97-mp3-kids-3/?lang=de
(so actually I would have to say YES, you could theoretically plug in / connect the mic at the headphone jack, but that won't do you much good as you can't record anything with it ;-)