Yeah, but there's endurance strength, maximal strength, explosive strength, etc.
In my example, carrying a kid around for long periods of time, endurance strength is a bigger factor than it would be if I was doing deadlifts. Plus, if I carry the kid again and again my muscles (not to mention my ability to balance, walk, etc.) will eventually adapt to the specific demands of carrying a 30 lbs. kid in my arms in front of my chest -- the posture involved, keeping the kid upright, etc. So the activity becomes easier.
So all I'm saying is, barbell training has given me a good starting point to carry the kid, but it's not perfectly matched to the demands of the activity.
Edited to add:
Let's say you could magically take two identical dads and have them train on an identical barbell routine with identical poundages on a routine that emphasizes maximal strength -- a 5x5 or SS, let's say.
And, we'll have them each do one supplemental exercise. One will do car pushes, the other will walk a half-mile carrying a 30 lbs. sandbag in his arms.
After six months of this regimen, each dad is put at the front gate of Disney World's magic freakin' kingdom and handed a sleeping 30 lbs. child. Each dad must carry the child to the busport, hold the child until the bus comes, hold the child on the bus, and then carry the child back to the Disney resort cheap-o hotel where you're staying. All of this must be done without dropping the child, and while minimizing the number of times the father has to set down the child to rest, or stop walking to rest.
Which dad do you think will perform better at this task? My money's on the dad who trained with the sandbag, because his muscles, nervous system, etc. are better adapted to that exact task.
So, in this context, the dad who trained with the sandbag has strength that's a bit more functional than that of the other dad.
But what's "functional" is totally dependent on the demands of the task.
