Third row means no tether strap, and it is difficult to access to strap the child in. Just as important is that three kids usually means bringing along all their stuff (strollers, etc) and there is far less storage space behind the third row.

Three car seats means a minivan from a practicality standpoint unless you can fit them in the second row.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue