There are a ton of baby-related issues that they don't directly address - such as diaper maintenance... and tell me how they're surviving without a swing or exersaucer!!! haha - just kidding.
You know, we don't ever really see any of them eating much, so it just must not make for a good story line for them to sit and feed a baby for 20 minutes. I know it's some of the least exciting parts of my day.
And someone has to mention that Aaron was as big as a 3 month old at birth, and looks now more like a 5 month old than a 5 week old. But again, such are the ways of television. All the "magic" they can produce with special effects, but we still can't have a baby who looks like an infant.