I used to work with a young chap (about 3 years old) who did this all day long at home - his mother would get quite upset by it. At school however, this behaviour was totally ignored and he only did it for 1-2 days then never again at school as he did not get the reaction he would get at home. It was certianly behavioural for this particular child (I wouldn't say attention seeking, but more to get his own way). Ignoring it and not making a big deal about it (minimal reaction) worked very well in this case but I agree that it would be worth looking at why it is occuring in the first place. I suspect there might be a sensory component to it given their age.