Raising singleton pups is different from puppies with litter mates. The puppy who doesn't grow up with siblings will miss out on some important life lesson like bite inhibition and dog/dog communication. He will be way more humanized than most puppies and may be prone to seperation anxiety where his people are concerned. Only puppies, a lot like only children (that me LOL), also tend to be pushy and bossy towards people. They didnt ever have any compeition for food, or toys or anything in those first few weeks of life and so they don't understand when something is denied to them. It's more work to raise an only puppy and they aren't for everybody.
All that said, it ISN'T difficult to have such a puppy, just more work. You have to do double time with things like socialization, seperations, communication. Have younger children will make teaching bite inhibition all the more important. Really, like I said, it isn't all that difficult
You just have a couple of extra steps to take and there are no short cuts really. On the bright side the puppy will already wat to be part of a human family because other than it's mother people may be all he/she knows. Thats always a plus so long as the human family teaches the puppy very early on that it is also OK and Normal to be left on their own for short periods of time.
I've raised several single puppies, made a bit of a specialty out of it. Mr. Wonderful is the third such puppy to grow up in my home in the last. It's pretty common for tibetan spaniels to only have one puppy or one surviving puppy. Howie was the first and he is almost 9... so far so good. Wonder had brothers so maybe she doesn't count. She was to sick as a baby to spend much time with the litter, she was pretty much hand raised. YES she has seperation issues because I was a bad mommy and didn't do my job right. We've also had two others including Mr. Wonderful now.