I've gotta chime in on this one.
You want performance? Get the ST, plenty of room.
I was a little kid in the late 80's/early 90's, living in a family of 4 with one younger brother. Our family car? It was an '87 Mustang GT, which my dad claims is more cramped inside than my Sunfire is. We all fit in it just fine, it carried our stuff around. It went on long haul camping trips pulling a tent trailer and a small out board boat motor in the trunk. There is nothing wrong with a Mustang with a baby seat in the back.
The other vehicle was a '79 F-250 standard cab. That did make things a little too cramped but it was very rare that all 4 of us would pile in that at once.
There was no soccer mom mobile in our clan.
The point of the story is that you probably don't need nearly as much room as you think you do. Leg room is a non issue for kids in the back for at least the first 10 years of their life or more. Depending on the car it may never be. At 5' 11" I sat in the back seat of a 2012 Focus and my legs were just comfortable. This was with the front seat adjusted to where I would have it as a driver.
So you could go smaller and more performance, Or used, save some money any maybe gain some in performance.