We have found 2 dogs that we like but only problem is one is 8 weeks other is 16 weeks they both a king charles... The two breeders are really nice and have done all the usual test on the pups..

I have a toddler, so am worried what age dog would be best the 8 week old had been around the breeders children and the 16 week old has never been around children but the breeder has advised me that she is has been socialised toilet trained etc. What age do you think would be best? Thanks everyone

I don't see the two ages as being most important.
Temperament and a vet check or vet record is.
What would be best is a book on dog training, for YOU, the parents.
Then bring your toddler to visit each pup again, and tell your toddler to just sit on the floor right next to you, and let the pup sniff you both and get to know you. Tell your child to keep his or her hands folded in his lap for a few minutes, while you pat the pup. Roll the pup on his back and rub his tummy to see how 'agreeable' (submissive) to such a motion he is.
When you do get one of the pups, spend a LOT of time with your child and the pup. A LOT. It's going to be a time consuming job for you. Study books and online advice, and maybe go to a dog class. Remember - more of training is of the humans than of the dogs. And children need to learn a lot too, some of it obvious to you, like not pulling tails and ears, but plenty of other things too.