I think that it's fairly safe to say that when Elly got all wound up about how if Michael disappointed everyone everywhere by selfishly giving up trumpet practice, it would inevitably lead to his sleeping on a steam grate, she lost an opportunity to do something useful and tell him something that he needed to hear. This is because Elly's fear of appearing weak and dread of giving him an angle by which to mess with her has left Michael (and by extension his siblings) with the foolish misapprehension that since John and Elly are adults, they don't have to anything that they don't want to do. As far as he can see, they're free and don't ever have to be pushed around by authority figures who treat them like idiots and chattel and tell them lies about how every day is kid's day. It seems to me that Elly and John would have done far better to tell him that life means having to do stuff you don't want to do but have to. Of course, that would mean having to actually communicate with him as if he were a person in his own right instead of simply an obstruction.