I'm glad you noticed/brought this up, it's something that's mildly annoyed me for years: the ads with a model United Nations at a kid's birthday party or playing.
However, I would say that what you're seeing is much more common in certain areas. For example where we're at my neighborhood looks like that. We're also much more populous (LA County) and we're in a traditionally port town. So our neighbors almost all speak 2 languages, are varying shades of brown, my own house is biracial, and to find a 'white' family....lessee...there's on on this block 4 doors down. That's it.
When the kids play on my block, my biracial kid plays with 2 Peruvian American kids, a half-Vietnamese/half-Taiwanese boy, 2 kids that are half Indian/half-Iranian and the girl at the corner house is half-Mexican and her dad is white. There's that one white family 4 doors down, but their 2 boys are too big to play with all these toddlers.
So, her (and their) birthday parties look like an ad that we think is unrealistic, but weirdly, I live in this world. Yesterday however we spent the day at the beach with the wife's family and it was literally over 50 people where I was the only white guy (one husband is Indian too) so it is true that people generally hang out with their own and not in 'rainbow coalitions'
Point being, in urban (I mean really urban) areas such groups of friends are somewhat common, and advertisers may be making ads that, rather than trying to promote some agenda, are there to market to more dense populations (LA, NYC, etc)??