Not sure why I didn't think of it before, but remembering when my boys were small, I'm guessing (1) refers to the red Teletubby, who was called Po.
Edit: Since putting the above, I've just looked up Po, and in terms of (3), it's the chemical symbol of Polonium.
Who is the connection between Harry Potter and Sherlock Holmes? (The answer isn't an actor)
I think we need a clue BB.Which 1966 top 10 hit song proved to be somewhat prophetic? (or- was rumoured to be so)
Had forgotten about this.These Boots Are Made for Walkin and the Vietnam War is all I can think of.