We have 2 dogs... 90lbs and 3lbs... they both have a time and place with the kids but are not free to roam while kids are in my care. Not for any fear, just more of a PITA to deal with kids hyping up dogs and vice versa.
If you are really wanting a dog i would speak with current parents and feel them out. If it is something that you really want there are always puppy pens while you are working.