You're not a snob for wanting your kids to have fun, easy playdates. Having children often challenges the relationships of even the best of friends. Different parenting attitudes have high stakes, because we all feel so protective of our little ones -- and deep down, we're often secretly sure our approach is best. It's natural -- but can be taxing on relationships.
This isn't the last time your friendships will be challenged by parenting issues. So take advantage of the fact that you and your friend have a close-knit history together. When it's just the two of you, take a deep breath and tell her it's been difficult for you to know how to handle it when one of the kids has a meltdown. Don't point the finger at her kids, but do explain that it's important to you to know, going forward, how you both will handle these outbursts. You can also say that you want the kids to all be good friends, so it's important they all have pleasant play experiences together. Talk about the good times you all have together, and say you'd like more of your visits to be like those. Then see how she reacts. Be open to what she says, and try not to be defensive.
In the best of circumstances, she'll take your comments to heart, think about it, and continue the conversation -- with changes in how she handles her kids. She may even have requests for how you handle your kids -- try to listen. But if she doesn't respond well, you'll have to re-evaluate how much time you spend together.