The only reason I can recall anything is because the words that I use to try to recall it ("what did I do yesterday morning?") take me down a chain of associations that hopefully will spit me out yesterday morning sometime, and that thing I remembered (maybe that I dropped one of my shoes when I was putting them on, or that one of my teeth hurt when I brushed it) can be a conduit to remember the rest of my morning.
The memory experiment just seems like spaced repetition to me [edit:which you can use to teach a cockroach, or a worm.] They show a baby a unique object with a particular use. The next time they show the baby that unique object, they either recall the particular use, or the experimenter demonstrates it again. As these periods grow longer and longer, the memories grow longer. The intuitive reason it would be less effective earlier in life than later is because babies can't see properly, or understand the positions of things in space, so they don't care when a mobile or a train moves; they don't recognize it as interesting.
Note: I can never remember what I did yesterday morning, because with the way I process the world, there's usually nothing in the sentence "What did you do yesterday morning?" that would associate with a particular day; every morning is yesterday morning. If I'm celebrating having done something significant "yesterday," however, I can start with that thing and work backwards to how I prepared for that thing. Some people are journalers/diarists, or heavily scheduled, and knowing what they have to do today, or maybe the last thing they wrote in their journal, would bring up almost immediately the memories that I have a huge difficulty recalling.