Listening on the extension phone generally not viewed as interception?

A reader sent me a link to this law review article which says courts mainly do not find a parent's eavesdropping to be a violation of the Federal Wiretap Act. The first footnote cites these cases: Schieb v. Grant, 22 F.3d 149, 154 (7th Cir. 1994) (acknowledging father’s use of an extension phone to record minor son’s conversations with mother permissible under the Wiretap Act); Newcomb v. Ingle, 944 F.2d 1534, 1536 (10th Cir. 1991) (holding interception by custodial parent of minor son’s conversations with father outside the scope of the Wiretap Act); Anonymous v. Anonymous, 558 F.2d 677, 679 (2d Cir. 1977) (stating husband’s recording of wife’s conversations with minor child excepted under Wiretap Act).