Honestly, IMVU says it has parameters in place for childrens' safety (17 and under can't chat with people 18+) but that doesn't stop people from making fake accounts.
If it was me, I would have a talk with my child and be completely honest. Basically tell them there are good and bad people out there. They can have fun and enjoy IMVU and it's public rooms, but as soon as someone is making them uncomfortable, leave that room. If someone is messaging them that makes them uncomfortable, block that person.
You hear outcry from parents like, "Why won't IMVU do something!?" Well we ask you parents, did you tell your child to leave the situation or tell them to block the person? "Well, no." My case in point.
If you are a helicopter parent, and can't leave your child alone, or if your child is younger than a teenager, I would not recommend IMVU, but that's just me. I've been on since I was a freshman in High School. I've met and seen weird people and as time went on, my blocked user list would grow. Just be wary and pay attention. NEVER GIVE OUT PERSONAL INFORMATION! EVER!