my son will be three in july and will not sleep though the night help!

my oldest son is two and will be three in july and he will not sleep all the way though the night, at least not in his own bed. when it is time for my kids to go to sleep he will go to his room, but around the same time every night he is up. if i am awake at this time i will put him back in his bed, when i am asleep i dont hear when he comes into my room so he will crawl up into my bed with out me knowing i have put up a gate before to keep him in his room but that doesnt work he eaither pulls it down or gets something to climb over it. i just dont know what to do i need some advice.