You know that isnt too bad an idea getting them signed up for activities it does keep them busy, it sounds as if they are in competition for your "Favors, meaning each in their way is jealous of the attention the other gets from you, your older Child was jealous when the younger sibling was born now they have joined up to be jealous of the little one, oh yes they love him but it has still taken more of you away from them. Get Dad involved a lot have him look after and play games when he comes home, outside activities, weather permitting in the winter. Set bounderies and say no TV No PC no reading or playing till ,teeth are brushed and ignore the demands for snacks if they yell plug your ears, better still no snacks in the house when you shop tell them "I ma buying no more snacks till you get the rules of the house and Family, they may not always put a toilet seat down however the big Boys arent too good at that! Use the time out method and be consistant,