I currently have a BMW X3 and a 4 month old. The gas mileage is poor(14.5) and if any more children come along the X3 will be too small.
The only car I have found that will get 20mpg and seat six for under $30k is the Mazda5.
Do you all recommend the Mazda 5? and what is your actual mileage?
I think that the 5 could be a good alternative for you. The interior will be a bit more spartan than the X3, but overall, the 5 is well built and well put together. One thing to consider is how many children you are thing of having. I currently have 1, and we plan on having another, though I think a family of 5 may be a bit tight in the 5. Thankfully, roof racks and a cargo box are easily obtainable.
Mileage will vary depending on where you lie. My wife primarily drives the 5 in a 50/50 mix of City Highway and it gets 25-26MPG. A few times that we have driven only city, it has dipped down to more like 20-21 MPG. On the highway, even with 5 people on board, we tend to get about 30MPG. The rang is probably 27-32MPG and is highly dependent on speed, terrain (hills) and head/tail winds. If you are keeping a 5 at 60MPH, 30+ MPG should be easy (and we only have the 4AT).
One thing you will probably appreciate coming from a BMW is the ride and handling of the 5. It really is a step above most small wagons/SUVx/CUVs and makes you want to seek out the windy, scenic routes (which ironically help the gas mileage due to lower speeds).
About the only faults I can think of is that the 5 isn't a drag race king. I has a very good, smooth powerband, but if you are out to race at stoplights, it probably isn't going to pull away from the pack. That said, it pulls smoothly up to the redline and had a decent kick to it. I have driven several 2-lane roads and it has good pick up for the 60-80 passing sprint. again, you have to pull out and floor it, but never felt like I was in danger passing (always plane for enough space though.... don't want to talk about how I learned that lesson).
Anyway, sorry for the novel, but hopefully it helps you out.