I have a 5 and.4 year old.
So they generally amuse each other, when not arguing or fighting.
But 5 year old likes Lego, screeching, dinosaur s, screeching, dancing, screeching, jumping, screeching, ponies/castles, screeching, playing on the tablet, more screeching, role play/dress up, more screeching... You get the gist.
The 4 year old likes Lego, ponies, babies, "making mummy a brew", bubbles, drawing, play dough, water, knights, trains, cars, stories, dinosaurs, pirates, anything to do with elephants.