The amount of information a new puppy takes in just in one day is phenomenal. Much of the exposure to their new world happens without us even trying. The exhausting part for me is making sure that all of that exposure leads to something positive, or at least neutral, for the puppies. Usually this means setting up the environment and directly supervising so I can intervene quickly.
Everything is new to the puppies - new house, people, dogs, car, smells, places, routine, potty areas, etc. Plus it's important to introduce them to things now at this young age that they will be living with for the rest of their lives. When introducing them to something new, it's important to go slowly even if you don't think the puppy will be bothered by it. You don't know for sure how puppy will react. Better to break it down into smaller pieces if you can, to ensure a positive experience. The puppy's behavior will show you when he/she is ready to proceed further.
In addition to leaving mom and littermates, coming to a new house, riding in the car, meeting new people and dogs - what else have they experienced this week?
Collars and leashes
Toys - lots of toys!
Pottying on leash
Being held and carried
Surfaces - grass,gravel, sidewalk, bumpy rubber mat, linoleum, carpet
Paddling in a couple inches of water in a kiddie pool
Eating dinner from a Kong
Ice cube treats
Playing with new adult dogs
Whew! Most of those are things that were just a part of moving into a new home. Their puppy minds must be swimming with all the new information! It's important to allow puppies plenty of time to sleep. This allows their minds to rest and digest all the new information. Their brains and bodies are developing so fast at this age, that they do need their sleep. And ... new puppy parents need that time when puppies sleep to get things done (or to nap themselves!)