Well, both dogs will require toilet training, recall training, etc. You talk about the springer as if it's hard work, with all the training required. The lab pup isn't coming to you fresh out of the box, ready to go either. The work will be just as hard with the lab pup, OP. No dog is easy street. Being 'well-bred' won't give you a get out jail free card. 
Training is everything... whether you get a 5 year old kitchen sink mix or a 'well bred' pup.
I would say, either way, you will have to be totally dedicated and you will have your work cut out for you.
We have a lab-vizsla cross, so I can't really comment other than labs are very food-focused.
My dog doesn't have this issue but I've looked after a lot of labs: they are foodies, especially chocolate labs. This is something you'll have to watch because they can, even with training, grab your breakfast off the table, the ice cream out of a child's hand, etc. It's cute and funny in when you see this in films but that behaviour can be relentless and exhausting in everyday, real life. That said, they are lovely dogs and the foodie aspect of them can be worked on, but it can take a while.
Springers are wonderful dogs, high energy, but lovely. I'm partial to both breeds! You know, you'll have to walk either breed for at least- at the very minimum- 1 hour a day. IMO, an hour is not enough. A walked dog is a happy dog. Whether you have a lab or a springer, two hours a day is great. Try and do an hour and a half a day, at least. The lab pup won't be up for long walks until it's older.
With ANY dog, training has to start from the get-go. You have to be consistent and persistent. So whether you go with the lab pup or the springer rescue, you'll- as I said above- have your work cut out for you.
Because of your children's ages, however, I'd go with the pup.
Good luck!