Hello there ... I have had a career in teaching from ages 4 through to 65+ - in primary, secondary and further education. Whilst I feel sympathy for you, I can, from experience, say that anyone who is being taught something and then begins to mess around, does so because their interest is not being held. Regardless of age. That sounds rather cold - it's not meant to be - attention spans of children (and adults) are getting shorter and shorter BECAUSE of the new technology which they can change to suit their attention at the click of a switch. They can't do that with a human being. Also, dependent upon what their home life is like, they probably have not been taught 'how to listen' or, even more importantly, how to concentrate and talk ... hence they would not have been taught how to think about other people either. Add to this the constant 'noise' that is all around us today (where do you go for peace and quiet - the only place I can find is the local church and even then they've started to play music now)! Into all this mish mash then comes the ability of the teacher/the excitement of the children at seeing someone different ..... where was the teacher during this time.... anyone worth their salt would have organised the class and the children so that there was time to give you chance to talk/demonstrate/answer queries...
Please don't give up on them, all children need to experience things other than this narrow curriculum they are now having shoved at them ... and for some of those children in the classes you visit, your topic might be the only thing they learn about which really interests them and then can set them on a different path for learning overall........ the pebble dropped in the pond sets up many ripples and is only constrained by the limit of the hole it is in. Bless you.