Question about a negative asset balance for a consolidated subsidiary

Say ParentCo acquired a 67% interest in ChildCo in 2015, and reports the investment as an Other Asset called “Investment in ChildCo” with the following balances as of December 31 of the following years:

2015: 400,000
2016: (150,000)
2017: (300,000)
2018: 325,000

Has the value of this asset been impaired between 2016-2018? I’m struggling with the vocabulary to describe what I’m seeing here, as well as the underlying economics of the situation. Any advice would be massively helpful. Thanks!

UPDATE: I found the following publication by PwC to be extremely helpful, and I do believe that this investment was impaired. However, any further insight on the subject would be appreciated, and I hope this helps anyone else with a similar question in the future.