Not blurry so much as moving objects

On the whole I am totally impressed with this camera, my first digital. I don't get blurry photos so much as problems with the subject moving ever so slightly and wonder if this is what users are referring to. I know I haven't moved the camera as I can get most of the subject in focus but one person might move. I have a number of photos where someone has moved an arm or started to look at someone else. One in particular is of my husband playing the guitar and two young sons watching. One child is so excited he is wriggling on his bottom - he is the only one with motion blur. I usually have the camera set on ISO400. I haven't yet studied up on using the camera on manual so all the photos I have are using various auto settings. Any ideas most welcome.