Arnold Barker starts every day by going out on his porch to pick up the milk and the newspaper but on this day he brings in something different — an invisible alien baby who's been left on his doorstep!
Acting
Alan Alda commits to invisible baby reactions like his life depends on it
Practical Effects
1966 invisible baby effects: blankets, strings, and chaotic energy
Production
Thirty minutes of pure 'we made this in a weekend' television magic

Director
Gene Nelson
Trivia, insights & behind the scenes
Gene Nelson directed this the same year he was transitioning from actor to director, and it shows in the 'let's just try stuff' energy.
This aired during peak 'domestic alien' sitcom era — The Invaders, My Favorite Martian, and now... whatever this is.