OP I would really not recommend a dog with a small family - we got our dog first so we can’t get rid of him but in all honesty he is more work than the children put together.
and if you must get a dog then I really wouldn’t get a puppy.
Getting two walks a day, in all weathers, everyday with small children is bloody hard work.
You think, great, I’ll combine a trip to the park so the children can go on the swings - but that doesn’t work - dogs can’t go into the big with the play equipment and 2 year old children don’t want to sit in the pram and be walked around for hours.
You think, great, we’ll walk to the shops / library, everyone wins....except you can’t because you can’t tie the dog up outside the shops in case it’s nicked and used for dog baiting.
Or, and I like this one the best, you think ‘it’s a lovely day, we’ll go to the pub, it’s dog and child friendly’ but it’s not really. Dogs are only allowed in the bar, children are only allowed in the lounge. So then you’re in that miserable family stuck outside breastfeeding on a bench in the rain.
If it’s hot you can’t leave the dog in the car, so no combining a walk with a cafe while the dog waits in the car.
And don’t get a dog that sheds hairs or you’ll spend your life hoovering.
I bought a fancy Dyson hoover to help with this - and now I need to replace the grouting in my bathroom floor cause it’s been sucked up. 
And the cost! Insurance, special hypoallergenic food, new carpets because the dog hates fireworks and digs when stressed.
And, finally, the bloody poo. It has to be picked up every time from the garden or a child will find it and step on it. Like magnets my children are to falling on poo.
Dogs are really enjoyable but not when karting small crying children around. You could add another two children to your brood instead - costs about the same.