Parenting is hard. You're on 24/7, and the "instruction manual" is lacking details (I don't recall the Bible discussing potty training). And if you mess up, you mess up someone's life--not something to take lightly.
One thing that's helped us is parenting partners. When Henry was 2 and Harmony was a newborn (and for the next year or so), we regularly hung out with the neighbors across the street. Since we've been back from sabbatical, we've done a lot with Jen's family, and more recently, the family who lives upstairs.
What's great is that we have someone to share frustrations with, bounce ideas off of, and trade childcare. For example, last night we had seven kids at our house--our two plus Jen and Charlie's girls and the boys upstairs. The kids had a great time, and it allowed the parents to do important things without helpers. (Believe me, we've had our share of kid free time in return!) Sometimes kids will listen to another trusted adult more than their own parent, and if we can help foster those relationships with people we know and trust (instead of with a stranger down the street, who we may or may not agree with), all the better!
Things that help make it work:
1. Kids of similar age. They don't have to be *exactly* the same age, but similar enough that they play together.
2. Similar parenting philosophies and strategies. Once again, they don't have to be exactly the same, but they're similar enough and compatible enough that we have common ground rules.
3. Similar schedules. The family we used to hang out with, we don't spend as much time with them because their life is on an earlier schedule (they're heading to bed when we're heading out to play).
4. Geographic proximity. Henry is loving having the boys live upstairs (though it may be a little TOO close--they want to play every second of every day!)
So what works for you?