I was 8 1/2 years old then and I remember this a bit. To me and my parents, this wasn't a first since the private school that I went to had a few negro students; we interacted with them and their families, but this was pretty rare at that time.
Jackie Robinson playing baseball all that year was an incredible event and it really had a huge impact on US society because of the visibility of the situation. A year later in 1948 President Truman signed an Executive Order that started the integration of the US armed forces. It wasn't until 1954 that the Supreme Court ruled that separate schools were not equal and therefore unconstitutional.
Jackie Robinson wore Number 42 on his uniform and a few years ago Major League Baseball retired his number. On a portion of an outfield wall at Fenway Park (not The Wall) in addition to the numbers of the five Red Sox players who are in the Baseball Hall of Fame, number 42 is placed there. Tomorrow a number of players on each team will wear number 42 and all the players at the LA Dodgers will wear number 42.