Arizona doesn't want kids, she changes her mind, she and Callie stay together (at least until later)
Christina doesn't want kids, suddenly Owen needs kids even though it never came up before, they broke up
Violet doesn't want kids (and during the conversation someone says that it makes her less of a woman), she changes her mind when she has her own, she and Pete stay together
Sam doesn't want kids, he and Addison break up
Charlotte doesn't want kids, she changes her mind, she and Coop stay together
And also there are a lot of issues with gender in terms of parenting and how mother always equals doing most of the child care and fathers are just babysitters (Callie and Arizona with Mark, Meredith with Derek). And if a couple with a child breaks up, the child always stays with the mother (Violet/Pete, Meredith/Derek).
It really seems like Shonda both buys into gender norms about children and believes that everyone wants a child and if they don't their partner does and will break up with them over it.