I am FAR from an expert in diagnosing Dutch Elm Disease, but most of the trees I've seen with it are well beyond the sapling stage. Most of the ones on my property were 4-6" DBH before they started showing signs ans dying off.
BTW - I planted 2 Princeton American Elms (bought from Home Depot) about 10 years ago. The are growing well and seem healthy so far. They were about 1" saplings, 8 feet tall when I planted them. They are now 6" DBH, and have shot right up in height.. I do wonder if they are really American Elms, however. The bark looks different than the American Elms that grew here wild. (I went to college at Princeton, so I probably passed by the granddaddy of my trees on numerous occasions.)
Correction: As near as we can figure, we planted those trees in 2008 (or so my wife says), so they've been in for 8 years. They were 1" or 1.5" diameter and about 8' tall when we bought them (they fit lying down inside my minivan). One is now 9" DBH, the other is 10.5". They are between 40 and 45 feet tall and show no signs of stress. It did take a couple of years for them to take off and really start growing.
Thanks for the comments. The reason that I thought that it may be Dutch Elm was because of this comment in the attached link. The other three trees are doing fine. They are being watered. We shell see what happens. I purchase the trees from a website called The Botany Shop.
"The first evidence of Dutch elm disease is wilting or “flagging,” leaves on the infected branches turning dull green to yellow and curl, finally becoming dry, brittle, and brown. The symptoms progress down the limb and eventually throughout the entire tree. If bark is peeling off the infected wood, the water conducting vessels will reveal the brownish staining caused by tyloses."