My son did the same thing from the age of 2 until 4 (so he's younger than your son). This coincided with my marriage ending so there was often just the two of us in the bed and sometimes I tried to get him back in his own and sometimes, when I was too tired or just liked having him there, I let him lie. Eventually he stopped doing it by himself but I have no idea if this will be the case for you. Do you know why he has started this trick? Is he anxious about anything?
CHANGE A LETTER GAME 16. Words of 7 letters , 1 or 2 changes allowed