Some more information would be helpful, as your needs are somewhat contradictory. You say fuel economy is a priority, but you are requesting something with 6 seats, which generally means a 3 row SUV or minivan? There is really no reason to jump to a 3 row vehicle with 1 child. A little more information on your needs would be helpful.
In general, if you must have 3 rows, a minivan will be much more efficient than an SUV and possibly more reliable given there usually isn't an AWD system to maintain. Maybe find an older Odyssey or Sienna.
If the 6 seats was a typo, than consider a small hatchback as it will be easier to get baby gear in and out. A used Mazda 3 would be a good reliable choice.
Congrats on the newborn!