Seasons 1-2 have the same opening title using the "Rise and Shine" theme song. But it is the closing credits on these first two seasons' worth that is really more wrong, that I hope a future BR re-release will correct. Seasons 1-2 only have the end credits from one of the season 1 episodes pasted all over.Many Flintstones episodes have the incorrect openings on DVD.
Season 3 was the first time, starting with the third episode "Barney the Invisible," that we heard the familiar "Meet the Flintstones" theme music for the opening and closing. On this version, the work whistle is the actual bird's screech sound (not a real work whistle like we hear on the opening title for seasons 4-6).
Season 4 was the first time we saw Pebbles in the opening titles (she debuted late in season 3, on the episode "The Blessed Event"), and for the first time, we hear an actual work whistle sound coming out of the bird. This is also the only version of the intro where we see Pebbles playing with her "Building Boulders." This season also marked the debut of Barney and Betty Rubble's child, Bamm-Bamm, whose debut episode was "Little Bamm-Bamm" and would be seen alongside Pebbles in the season 5 opening title.
If I get this right...
Season 3's opening title has the work whistle bird screeching like a bird.
Season 4's opening title changes the work whistle bird's sound to a real work whistle, and Pebbles is seen for the first time, initially seen with her "Building Boulders."
Season 5's opening title is the one where Bamm-Bamm debuts. We see the Flintstones take Pebbles and Dino, followed by them picking up the Rubbles, their son Bamm-Bamm and pet Hoppy. The opening title finishes off with Pebbles and Bamm-Bamm placed on Dino's head.
Season 6's opening title is slightly re-scored by Ted Nichols.
Some season 6 episodes use a different closing theme, this one with Pebbles and Bamm-Bamm singing "Open Up Your Heart (and Let the Sunshine In)." In reruns, the first episode to debut the song -- "No Biz Like Show Biz" -- uses the standard "Meet the Flintstones" closing theme instead, but two other episodes, "Royal Rubble" and "Fred Goes Ape," retain it.