All puppies are pretty hyper, by any measure -- it would be unusual to have one that is quiet and laid back (if too quiet, I'd worry about a hidden health issue or temperament issue -- eg too shy). A cavalier is often a more laid back ADULT breed than some others but not any more so I would say than those other breeds. And a puppy is never going to be laid back especially once they hit about 4 months and they will be go-go-go-go-go and also chewing everything they can get hold of and into everything. All puppies also go through a people nipping phase that can hurst children and needs to be positively but immediately managed to train for a 'soft mouth' (all in Ian Dunbar, below).
If you want a quieter puppy -- ask the breeder to recommend the one to select, don't take 'the one that comes to you' as it will be the most outgoing in the litter. But this is a terribly tricky area as a quieter puppy could be deeply unhappy and overwhelmed in a noisy bustling family atmosphere.
I generally do not recommend families with children under 7 to go for a puppy -- but instead aim for an older dog, at least 6-9 months but a year or two old and known to be good with children is much better and a thousand times easier. A lot that is damaging to children and to puppies can happen in that first year and puppy cuteness soon is gone making getting a puppy a pretty ephemeral thing. I also always warn that adding a puppy is going to be the same work as adding a toddler to a family -- it will require a tremendous amount of time and work that cannot be ignored -- or the results are generally poorly behaved adults (this is likely the case with the very hyper pug puppy). Families -- and most owners in my experience! -- greatly underestimate how much work and how great a time commitment a puppy is.
In general: Much depends on the individual dog -- just like children.
All personalities vary. Then much -- MORE!!! -- depends on the family, how controlled the interactions are with children, and how much time the family puts into proper, rewards-based training (eg never punishing a dog but instead working to positively train towards what you want in an adult).
If you are sure you want a puppy: then be sure to read Before You Get Your Puppy right away, a free download from internationally known trainer Dr Ian Dunbar.
At the same link you can download for free, his After You Get Your Puppy.
Both of these books will prevent a lifetime of problems and also help you decide if a puppy is the right thing for you and your family.
www.dogstardaily.com/free-downloads
I also have a link to a good collection of links on managing dogs and children, pinned to the top of the training section. That's another must-read.