Toddler grew up and Imaginary Friend won't

I know this is old, but I'll tell you what worked for me, just in case anyone else is having this problem. While the child is still a toddler, you have to name the doll, and decide whether you want it to be a boy or a girl. Once you've done that, you just put the doll on the ground while your toddler is aging up, and the doll comes to life as an imaginary friend that only the child can see. Sometimes it takes a couple minutes, but it should happen pretty quickly after your toddler ages up. If the doll was in the sims inventory when the toddler aged up, and it doesn't come to life when you take the doll out of the sims inventory, try having the sim leave the lot, but keep the doll at the sims house, then come right back home. This will typically make the doll come to life. I've had this happen after my sim went to school several times.