How does Davey's brother, Dennis, represent the theme of need in the novel, Gypsy Davey?

Baby Dennis is perhaps the saddest figure in the book—sadder even than Davey, because Davey has a means of escape with his bicycle. Dennis, representing the theme of need, must rely on others for every creature comfort. No one, with the exception of Davey, is responsible enough to fulfill his needs, and Davey is allowed to visit Dennis only occasionally. Dennis suffers from lead poisoning from eating chips of paint off his crib (though no one ever thinks of removing him from the crib), and there are indications he has other physical or mental problems. Davey talks about how the baby "stops still and stares for almost ever" and "moves funny sometimes more like a praying mantis than like a big baby boy." Even Davey's attempts to help the baby, though well intentioned, are probably hurtful: for instance, he feeds Dennis Bavarian cream doughnuts instead of nutritious food. It is as if Dennis is the vessel for two generations' worth of irresponsibility and despair.