As soon as your little one get into your bed, get up and take him/her back to his/her own bed, only saying something like "you must sleep in your bed" and that's it. Even if this happens 20 times, your little one must know as soon as he/she gets in your bed, he/she will be taken back to his/her own bed. Keep every calm and relax while doing it, after the third time, don't say anything, just take him/her back to bed. Don't go and lie down next to him/her, when you do it once, you will have to do it the next time and thereafter its something permanent. You decide how things will go, not your child. This really works, you must just be patient.