The usual problem with walls in war is that they are manned, and as you climb it, they drop rocks, boiling water, melted led or pitch on you and set you on fire. If you instead could just teleport up and start a fair fight the defenders advantage is reduced significantly.
You are of course right about the curtains. I bet Eladrin cities had the best curtains ever!
Kinda sorta though. For one, again, it's a maximum of 25 feet. That's a pretty low wall. Certainly not a castle wall. And, since we're still requiring LOS, the best you can do is teleport pretty precariously on the top of the crenulations. Easy pickings for defenders who just need to give you a bit of a push and splat you go. Remember, a 25 foot teleport is less than three stories. We're talking a second story window at best.
If we actually are talking about 10-15 foot walls, by the rules, anyone can climb that in one round (climb is half speed). Granted, more difficult, as the climb DC's would be tricky, but, again, anyone who brings a ladder is doing the same thing as the Eladrin, with the added bonus that he can bring that ladder up and climb down the other side as well.
Where I would really see the impact actually would be on the battlefield. Being able to move an entire unit laterally 25 feet is a huge advantage. Imagine how easy it would be to avoid a charging cavalry line. Teleport over the line and hit them from behind while they try to turn around. That would make cavalry very difficult to use against Eladrin.
As far as teleporting babies go, well, for one, small babies couldn't teleport much at all, since they cannot see far enough. But even somewhat older children would likely have enough sense of self preservation not to get killed. After all, our own children manage to survive into adulthood despite all sorts of dangers. I'm not sure that Eladrin children would be that different.