Since you asked about Lafayette, I'll confess I am a fan. I like the small town atmosphere of Erie, Lafayette as well as the Frederick-Firestone communities. Lafayette has a few nice restaurants of its own, but you'll be close enough to Louisville and Boulder for afternoon and weekend drives.
Another possibility: Have you heard that a company is planning to construct a monorail service between Longmont and Boulder? Longmont is approaching the size of Boulder, but it is more of a family-oriented community. Evidence? My three teenagers couldn't wait to get out of town when they started driving. But, I love Boulder for all it has to offer, too. (Actually, there is plenty for teens to do here.)
Erie has a plan for a large development working through its approval process, and it could become a much larger community. http://www.dailycamera.com/erie-news/ci_24269978/erie-oks-an
Lafayette, which has Boulder Valley schools, plans to remain distinct from its close neighbor, Louisville. RTD says they will run light rail up through Louisville, but that won't happen for decades.
Longmont and Louisville have been working diligently to improve their old town centers. Both communities are encouraging art galleries, restaurants and small concerns to locate in their downtowns. Things turn busy on weekends. All of these communities serve an active lifestyle. Boulder has excellent schools, and Longmont's schools rate high, too.
There's more. Visit my blog for a large list of parks, recreation areas and trails. Some of these areas need work after the flood in September.
We did a lot of picnicking at Boulder Creek (behind the public library) when our kids were 4. (I had twins.) Dad would take the kids hiking on the trail up to Flagstaff. We took advantage of a lot of these parks and rec areas. Fun times.
New theaters are planned for Twin Peaks Mall in Longmont.
I could go on.
Best of luck to you.
I live and work in the Martin Acres Neighborhood. We have a lot of young families and a beautiful park (Martin Park) where many of us meet up regularly. In addition, Whole Foods, Kinkos, DryCleaning, Liquor Store, Noodles, Beau Jos Pizza, etc. is just a short walk from our neighborhood. From my house it is about 10 minutes (walking) to all of these and the north edge of the CU Campus. Our nanny is a CU student and she loves the easy commute as well, often she rides her bike or walks. Ours is just one of many neighborhoods that would meet your criteria. Arguably, Martin Acres is one of the more popular hoods because of the proximity to all the amenities, including bus stops and it is considered "entry level" in terms of price for Boulder. Let me know if I can help answer more questions or provide any more info.
There are a lot of great neighborhoods in Boulder that should meet your needs. "Quiet" does not always describe the neighborhoods right around CU (especially on a Friday night), but you don't have to go too far for things to settle down a lot.
The immediate downtown areas may be a little too pricey because everyone wants to live there, but again, you don't have to move too far before you see rental prices drop. Boulder is, after all a relatively small town.
If I were you, I would think in terms getting easily to places like CU and downtown Boulder quickly and conveniently. Among other things, Boulder has an amazing bike path and bike lane system. For example, you can live pretty far north in Boulder and ride straight down the Folsom St. Bike lane to campus or make a right turn at Pine St. and head downtown,staying in another bike lane. Sometimes you will be moving every bit as fast as car traffic. See link on the "Web References" line below.
You can find rentals on all the real estate websites, including this one. But you might also want to check out this site (and pay special attention to Ralphie's List, accessible from t link on the top right.
Hope this helps!
Congratulations on your growing family and your move to Boulder! Unfortunately, our rental market is really tight here. We had really low vacancy rates before the flood in September and now it's even lower. If you can find something available, $1,500 should get you a nice 1-bedroom condo or apartment in Boulder proper. If you want a 2-bedroom or a house, you might need to look at outlying areas. Gunbarrel is an area just to the northeast of Boulder and rents there are generally lower. Louisville, Lafayette and Superior are other options that won't be too much of a commute. I live in the University Hill neighborhood of Boulder and sometimes I hear about places coming available for rent -- if you send me a message directly, I can keep you posted. Keep in mind that close to the University, property managers start "pre-leasing" in January for leases that start the following August.
Good luck with your re-location!
Visit my website at http://www.westrealtynoco.com and click on "Market Insider". You will be able to get all the information for Boulder and the various zip codes. This also gives you the opportunity to compare neighborhoods and all the trends and stats for various areas. Good luck.