My fiance has asked me to move in. After much kissing I said yes and a window popped up with possibles movers. As I have a toddler at home I selected her. The new thumbnail showed me but not my toddler in the family. I did not save the game as I don't want to move without my child. Why did she not move in too?

It sounds like you may have click on the toddler to move with you, but failed to click the arrow to add to the right panel... Hope that helps

Toddlers tend to take a while to show up, they usually come crawling or walking from a far end of the house after a few minutes

That is true too!!! I forgot about that. Good call Kherina.

I would go with Priddychild's first reply. Whenever I have moved a toddler, their thumbnails show up even though they sometimes show up at the far end of a lot.

Ok thanks for the advise. I will try again tomorrow. Perhaps I did not click the arrow.

I find when I move in new sims, like toddlers or whatever, it usually takes a few minutes for their thumbnails to show up, and for them to enter the lot

You were all correct, I did not click the arrow. After doing it I went outside and there was my little one walking towards me. I am so happy. Thank you to all of you.
Just out of curiousity, what would have happen if it had been a baby? Would I have found her lying on the pavement?

yep, sure would. A sim usually automatically goes to pick up the baby without being directed.

Also, the game will not let you move in if you are the only adult and refuse to bring your child/toddler/baby with you. It will give you a message saying they are not an irresponsible parent and cannot leave their child.