Hi Saoirse! I think most of us here would say to go for the 16 week puppy -- 8 weeks is generally considered very young for rehoming this breed's puppies as they are still so small (especially if there are any children around the home). Also, a 16 week old will be much more confident and on its way to housetraining etc. It seems a little strange that for a small scale breeder (if this is in Ireland, I assume IKC registered?) an 8 week pup would be exposed to kids and not the 16 week old -- why the difference? Are you sure they have bred these dogs themselves?
Keep in mind most good breeders won't rehome a dog into a new home right over the Christmas period, especially if there are children as the activity and strange people in and out, noise and activity can seriously stress out a new puppy or adult dog.
Breeders often say they 'test' but the actual tests they need to have done include cardiologist exams and MRIs and most have not done these. I cannot stress enough how important they are for breeding dogs due to the high rate of two potentially costly and serious genetic illnesses in the breed, which most do eventually get (though not all will be symptomatic or need medications). You can get proper info on the correct tests and the certs the breeder should be able to show you here:
www.cavalierpuppy.co.uk
We've got some good info on bringing a dog into a home with a toddler and young kids pinned at the top of the training section. These should be very helpful. To be honest, a toddler should be kept separate always from a puppy or adult dog anyway except for when an adult is right there managing the interaction at arm's length. It doesn't matter the breed, children tend to do things that easily cause dogs to get seriously stressed which can over time result in fear aggression or an immediate snap. A small toddler falling on a puppy by accident could seriously harm or kill a puppy as well. A puppy will need to be completely penned off from a small child (or vice versa) -- there's lots of info at the pinned links, from good trainers.
Hope that helps a bit. I would guess you are in the UK or Ireland and would just stress there are only a handful of properly testing breeders in these countries )or anywhere) so it is important to make sure a given breeder is one of them.
The fact that a breeder with supposedly only two breeding dogs has puppies so close in age available just raises some possible red flags. Responsible breeders and especially small breeders would only so rarely have litters close together, especially only two months apart. It suggests they are breeding for commercial reasons as well. I could be totally wrong of course but from a decade of experience of doing cavalier rescue in Ireland and working to tackle puppy farms and backyard breeders in this country, there are certain alarm bells and far too many breeders ready to dupe trusting buyers.