This will most likely take two playthroughs. You can get the most Crawlers in the nursery area. Slowly back up will shooting the heady with the Plasma Cutter. Just don't hit the orange bulb.
If they get to close or more than two are close together stasis them and pick them off one by one.
In the later areas you will encounter a few more crawlers, but at least 15 should be in the nursery.