Toddler not sleeping please help


My sons routine is so messed up

So he goes to sleep at 6pm for nap and wakes up at 8pm I try to put him back to sleep but doesn’t work and he decides he wants to play till 4/5am it’s driving me crazy he wakes up at 11am what can I do to sort out his routine I need him to sleep I feel like he m getting ill cause of this