Please, please, please consider contacting a reputable breeder and asking if they have any "retired" show dogs that they are looking to place in a pet home. These dogs are often "middle aged" (aka 2-5), because they were show dogs they have a been there/done that attitude, come already trained (house, crate, crowd, etc), and most would *love* to be an "only" dog! I have many breeder friends who have dogs like this to place, but none that breed collies, unfortunately.
Puppies are lovely, but more work than your three kids combined, believe me

. Plus they tend to retain much of the "puppy behavior" well into their second year. Too many new owners think that once the potty training is done, that the dog will act all grown up, but it really doesn't work that way! I have a 9 mth old that I have put TONS of time into, who would still rather chew on a table leg if I let him rather than a rawhide bone. (And this is after two rounds of puppy socialization class, obedience class, and beginning agility class!) Puppies are exhausting!
Think of it this way: you crate the pup during the afternoons/evenings while you're running your kids to all their activities. You get home late in the evening, exhausted, still have homework/housework to do, and now that the pup has had a good long nap, he's ready to play, run, stay active for hours on end!
Good luck with whatever you decide...
Terri