I've already mentioned this, but I guess it bears repeating. The biggest difference is the popularity of strollers and carrying your baby around in a seat. If you look at parenting across other cultures, you see babies are often carried very close to their parents face. This actually encourages infants and toddlers very early on to notice social cues when their parents are speaking to others. This is very important for socialization, and if you are being carried at the knee in a seat or stroller, you (the baby) do not have that easy access. The only time you are getting that social interaction is when your parent or their friends/strangers, brothers, sisters, are directly interacting with YOU (the baby) and making faces, talking in baby talk, trying to make you react (good or bad). So, that can cultivate more of a selfish (in a social sense) attitude since most of your early social interactions are between others and yourself, not others with others (i.e. your parents and someone else).