You will need an appropriately sized violin. Check my resources page for a list of good violin shops in the area. Renting is the best option, especially for small children. Please don't buy a violin on the internet. While there are cheap violins to be found online, they are difficult to play and won't sound good. You will get a much better quality instrument by renting from a good violin shop.
Start listening! This is so important; students will learn songs much more quickly if they have a regular listening routine.