We have a Whippet, he's fantastic with our children, DD is 7 and DS is 21 months.
We already had a little dog, a chinese crested hairless who we picked from his litter whe he was only a day old, we got him at 8 weeks old when DS was 4 months old so they've grown up together. We got our whippet last December and he fitted into the family realy well.
What I really love about our whippet is that he's so submissive, our little crestie is very much the boss dog in our house. DS also lays all over him and he just puts up with it. He's super chilled out when around the house but so much fun to take out for walks. He loves to run around in the fields near our house and is so fast.
Another great thing about him is that he doesn't shed hair and is completely odourless. You can actually bury your nose right into his fur and still not smell a thing.
When I said odourless, I don't mean the farts though, they're evil
The main reason we chose a Whippet over a greyhound is his size, we wanted a smaller dog so he could fit through a small dog flap to get into the garden. My friend was burgled because the thief got in through her labrador sized dog flap, whereas the smaller dog flap is only really accessible to our pets.