Aye, there's the rub. Money. And baby. As per Mike, congradulations. My kids stripped not one, but both screws off my Tascam 38 pinch rollers. So baby friendly works both ways, and doesn't end until far too late.
I've used both makes of boards and both are good. I'd be inclinded to go w/ the Mackie. The effects on the Yamaha might be OK for live work, but I always hate paying for such on a studio board where I have better options. I would think the mackie preamps would be a touch better if you plan on using them, tho the yamas suffice for live work.
And I definately check them out in person. The ergonomics will be important if you plan to live w/ the board for a while (hopefully not for 18 years when the kids should move out!) and the "feel" is probably more of an issue between the two than quality.
best of luck,
@
Edit - addition. the mackies can get kinda crowded if you have big fingers, so double check that