4" tall????
Sounds pretty streched to me
How many nodes do your plants have?
How far away from the light is it?
What type of light?
Need more info to correctly diagnose possibilities.
I had a seedling once that had a very flimsy stalk and couldnt hold its own weight. I shaved a couple flat pieces of wood, about 1/4" wide and 1" long, and stabbed them into the rockwool cube around the stem. This worked exceptionally well for me. I named that plant "toothpick" and kept that strain alive as it turned out to be the biggest plant, as well as the best bud growth.
So to sum it up, just try to prop it up somehow.