I'm the cases when I have heard the term used "Giving my testimony" had nothing to do with confession of ones sins and asking for forgiveness, but rather testifying to how God had saved you. That is the problem with making any blanket statement about protestantism per se because there are so many groups and great deal of varability in both believe and termonlogy even within a given 'group'.
there is for instance extreem diffrences between Lutherens who are members of ELCA and Lutherens who are member of the missoury sinod.
The first being extreemly libral and embracing everthing from homosexaual marrage and clergy to abortion. The other being decided anti-catholic and engaging in the buring of rock-n-roll records as evil my home town during the 1980's. My hometown actually had one of each kind of Lurhteran and they hated each other.
I've taugh 6th grade religious education for 2 years now and have found :
Most 6rh graders are studing world history, so explaining the differences between catholisim and prostenism in terms of how protestenism arouse historically is intresting to them becaus it connects to something else they already know. ( although most people students already spend enough time in the books , so too much detail will proably boar them.)
I like to point out the passages in matthew in which peter is declared the rock and explain that the catholic church is historically the church Jesus founded and that all protestant church's were in fact founded much later and that thier teaching were invented by later men because they did not want to obey the authority of the pope.
That gives you lots of good jumping off places , but probably shouldn't take up more the a few class periods.
You should definately go through the creed as recomended above and make sure they understand the sacraments and what they mean.
I like to give time for questions as 6th graders usually have plenty of them on thier own.
As always, RE should be about conversion so remember while it may be your mouth that is moving you should pray hard it will be the holy spirit doing the talking.