My niece has 4 year old twin boys, I encourage her to bring them over so my puppies would become accustom to the "small child" before I put them up for adoption. Socializing the little babies is a great thing to do if one can when rasing a litter.
The biggest reaction from the puppies to the children is ...fright because a child moves so fast it intimadates the puppy.
I have my grand nephew's sit on the floor in the confined room and supervise...but for the most part the puppies will be puppies and lick them to death
The biggest fear is when a puppy is sold to a family that thinks their child will be responsible and gentle with the puppy and if not taught how to hold or care for it they can easily hurt or even break something...
holding them by the neck
dropping them on the floor
stepping on them
sitting them on a sofa or their bed and leaving the room (leaving the puppy to jumping down by himself)
its what kids do and if not taught properly
another quick story...my 92 year old neighbor came over to visit the puppies very excited she sat in a chair and held one...she was so busy talking she forgot about the puppy, the poor little thing at 3 weeks old fell onto the floor from the chair.....Poor baby was screeming like she was dying I ran to pick her up (actually I really pissed off) thank god she was fine and merely scared from the drop.
bottomline when placing your babies make sure you trust the buyer will do everything possible to keep your babies safe no matter what the age, cause a toy is not a TOY!