Is it willful abandonment if I got the father's paychecks garnished and then later he disappears for 3 years and did not see the children in those 3 years but the garnishment still continued?

Abandonment as for as a reason to try and perhaps have visitation terms changed, yes it is in many areas. Abandonment in terms of a criminal issue, no,

In many states, paying support, even though garnishment is considered contact.

So what is it you want to do ? Change his visitation order?

The real question here is what do you want to do about it. You might find this sticky note helpful:

https://www.askmehelpdesk.com/family-law/child-abandonment-read-first-364259.html

If you have any further questions after reading it, please feel free to ask.