Love it! I used to go with my dad before I got married... He still goes with my DB. We always rent a condo at the Sundowner complex - its at the bottom of the 4 o'clock run so you can have a long, lazy ski home.
Shuttle to slopes leaves from the front of the condo. The unit we usually stay at is a bit small for 6, but I think they may have others. Anyhow, its on the 4 o'clock road, which is walking distance to town, too.
Will be trying it with the DCs in 2011. But Breck has loads of kiddie activities, too.
Breckenridge Brewery is a must for one dinner...
<sigh> Missing it now! Its a pretty laid back place, very nice.
OP, I really think you need to consider the baby here - you've got a fair handful of adults here saying the altitude was too much for us - but at least as adults we're able to articulate what's going on. We can blow our ears, buy some oxygen - a baby can't.
Breck is lovely, but Colorado just might not be the right place for you right now.
Being a killjoy I'd add to the comments of others re altitude. I felt sick as a pike the first time I went to Breck (which is a great place). Not sure I'd have it on my list until DD is over 2 - and even then the length of the flight + transfer would probably put me off; she has yet to develop her parents' love of travelling!