Your question is a first in the 2+ years I've been 'listening' on the Forum. Most folks want to get rit of them. So, from that angle, I'll give my unsolicited $.02 ...
Willow trees are notorious, for sucking up water. That's why you find them thriving along almost any waterway in any Zone in which they grow. At the same time, and in the same Zones, you MAY find then thriving near underground plumbing! Like septic systems, leaching fields, and even man-laid sewer and water lines. This is where the problems lie.
If your saplings are growing near any of the said man-made/installed structures, I'd destroy them. The root system is well known for crushing water lines, sewer lines, and so on. In My Humble Opinion, there's no 'safe' place to plant a willow tree on your property. PLUS, they're a mess when they see and leave. Some municipalities are cutting them down along waterways and such to actually conserve water. Granted, it's a double-edged sword when doing this. (I'll spare the details ...)
Well, you've got the drift of what I think of Willow trees. My best to ya and hope this helps.