I have a 98 OBW & my parents have a 98 Forester S. The biggest difference is the leg room in the back seat. The Forester sucks for anyone with long legs! The OB is wonderful. I can have my seat all the way back and a back seat passenger behind me who is 5'11" and have no probs! Not so with the Forester. Also, the width of the back seat is narrower in the Forester.
When we compared the ground clearance, we didn't see much difference, just fractions. I guess it comes down to what you are looking for and want. If it were me with a kid...I would go for the OB. More passenger room. Put your kid in both and let them decide which is best! Good Luck.