1. My earliest memory is from when I was just a bit shy of age 3. I was coming home from a wedding reception when my family turned on the news at our old house and I saw images of a car crash on the news saying a princess had just died. Later on in life, I realized that it was almost certainly the death of Princess Diana I was hearing of, and the date was Aug 31 1997. Thus, my memory has a defined start date, Aug 31 1997.
2. No, this is a very bad idea, according to child developmental psychology, it will have a massive detriment even if they cannot remember. In the first two years of life, a critical development period occurs, and one of the important things that happens is the child forms an attachment to the parents. If the parents are only intermittently present or are not, they may attach to someone who later leaves their life when their parents are back or even worse, don't attach to anyone. This can cause what's called Reactive Attachment Disorder, fears of abandonment and anxious avoidant attachment styles which can fuck you over for life. It's even been shown that children who fail to securely attach are more at risk for depression, alcoholism, personality disorders, drug addiction and criminality later in life, and this is often seen in children taken from Romanian orphanages who suffered extreme abuse before the first two years, before they can even remember.
In fact, while children can recover from abuse more easily if it began after age 2, if abuse began before age 2 they're often stunted for life sadly.