You asked

Our little one is in preschool. Is this a good time to get a family dog?

There is no right or wrong age to get a family dog; however, you should be mindful of your situation before you rush into things.
Waiting until your little one is at least three year old will mean that they will be able to get involved in the feeding and playing but remember, until your child is at least seven or eight they can’t be expected to take up much of the minding so it will become your responsibility.
Getting a dog is a huge responsibility and you should only ever get one if you feel you are ready for extra addition to the family. While your little one will benefit hugely in terms of physical fitness, social facilitators and by gaining a sense of responsibility, they won’t be able to do much more than feeding and playing so the burden will fall on you; remember, dogs take up as much time as children when they are young.
The best way to determine if your little one is ready for a dog is to see how they handle situations of responsibility already. Ask yourself - can your little one get dressed without help or prodding? Do they have compassion for living things? And do they become attached to things easily and then just drop them?  
If you do decide to go ahead and get a dog, you should choose one that is between the ages of one and five as animals in this age range are good with children because they are less excitable. Before you bring your new pet home make sure they are comfortable around children and that your little one will be comfortable around them.   
Getting a dog before our little one starts big school will mean that the excitement will have settled down by the time it comes to going to school and they won't be distracted but you should make sure that you are ready for pet and that you are not just getting one for your preschooler. 

More questions

There is no right or wrong age to get a family dog; however, you should be mindful of your situation before you rush into things. 
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