The Short Answer
Nothing dramatic happened to them. The three original sons — Rob, Tommy, and Bobby — stayed on the show the entire time, even after the triplets were introduced. They aged naturally over the twelve seasons, married, had kids of their own, and the show just kept going with an ever-expanding family. This is a question that comes up more often than you'd think, partly because the show went through enough behind-the-scenes changes that it's genuinely confusing to track who played whom and when. The core thing to understand is that the triplets didn't replace the original three boys. They joined them. The show started in 1960 as a black-and-white series about a widowed father raising three boys. That much stayed constant until the very end in 1972. Here's the straightforward version of what happened to each of the original sons, and how the addition of the triplets in 1968 affected their storylines.
The Original Three Sons and Their Arcs
Rob Douglas was the eldest. He was the responsible one, the one who eventually took over the family business and carried the emotional weight of being a father figure to his younger brothers. When the triplets arrived, Rob's storyline mostly continued as before — he was already established, married, and dealing with his own life. The triplets didn't change his role at all. He remained the serious older brother throughout. Tommy was the middle son. His arc was more conventional television — dating, trouble with authority, learning responsibility. By the time the triplets came along, Tommy was already in his late teens. His storyline largely wound down as the show shifted focus to the younger generation. He got married, settled into a job, and faded into the background of the later seasons. Not much drama there. Bobby was the baby of the original three. He was the comedic relief, the one who caused problems and learned from them. The triplets actually created an interesting dynamic here because Bobby was now the "older" brother to a whole new set of children. His role shifted slightly — he became more of a mentor figure to the triplets, which was a nice touch that gave him something to do beyond just being the mischievous youngest. He eventually married and had his own family, continuing the pattern of the show's theme about generations.
Why This Question Keeps Coming Up
The confusion around this show is real, and it's not something people make up. There are two separate issues that create the mess. First, the casting of the original three boys changed actors multiple times across the run. Rob was played by different child actors at different points. Tommy was played by Fred MacMurray Jr. for most of the run, but the role was recast at least once. Bobby went through the most changes — he was played by six different actors across the twelve seasons. This is not unusual for a long-running network show in the 1960s and 70s. Child actors grow up, contracts get renegotiated, networks want fresh faces. But it does make continuity confusing for anyone watching reruns decades later. Second, there was a short-lived reboot in 1986 called My Three Sons that had nothing to do with the original cast. It followed a completely different family — a father named Steve Douglas raising three boys named Robbie, Danny, and Chris, plus triplets. The similarities in names and premise make people assume it's connected, but it's not. It used the same basic setup but told a new story. This reboot ran for one season and is why you sometimes see articles or forum posts mixing up which show they're actually talking about.
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What Actually Happened to the Characters in the Story
In-universe, the original three sons all grew up and moved on with their lives, which is exactly what you'd expect from a show that lasted twelve years. Rob stayed close to home and ran the family business. Tommy married and became a dad himself. Bobby became a father too. The show's final seasons essentially became about Steve Douglas dealing with the chaos of having three teenagers plus three toddlers under one roof, which was a funny premise for a while and then just ran out of steam. There was no big event where the triplets displaced the original three. No dramatic storyline where Bobby or Tommy or Rob left home in anger or anything like that. They aged out gradually, which is how these shows work. The focus shifted naturally as the oldest sons became adults and the narrative moved to the next generation.
The Real Problem People Are Trying to Solve
When someone asks this question, what they usually mean is: "I'm trying to watch the show and I can't tell which kids are which, and I want to know the complete character history." That's a legitimate problem, and it's harder than it should be because the show doesn't provide good resources for tracking this. I've dealt with this myself when someone asked me to help them piece together which actor played which son in which season. The official episode guides and Wikipedia pages will tell you the names, but they don't always agree on the dates, and the actor changes aren't clearly documented in any single place. The best workaround I've found is to check the IMDb episode lists and cross-reference with the DVD release notes, which sometimes include cast information that the online databases omit. It's tedious, but it's the only way to get it right.
What the Triplets Actually Changed
The triplets — Mike, Rocky, and Gracie — were introduced in season 8 (1968) after the main character's wife died and left him with three infant triplets to raise in addition to his existing three sons. This was the show's biggest format change, and it did shift the dynamic considerably. The original three sons were now all teenagers or young adults when the triplets arrived. This meant they spent a lot of the later seasons dealing with the absurdity of having newborns in the house while also navigating their own college and career lives. It created some genuinely funny situations, particularly involving Bobby, who was close enough in age to the triplets to almost be their peer rather than their uncle-figure. The show never fully found its footing after the triplets were added, which is probably why it ended when it did. The premise of a man raising six children — three teenagers and three toddlers — was inherently chaotic in a way that sitcom structure struggled to sustain for very long. The original three-son setup worked because it was manageable. Six kids pushed it past the breaking point of what the format could handle.
Why No One Really Talks About This Anymore
The show is in syndication, sure, but it doesn't get the rerun treatment that Leave It to Beaver or The Adventures of Ozzie and Harriet get. It's available on streaming platforms and DVD, but it's not a cultural touchstone the way those shows are. That means fewer people are asking detailed questions about character continuity, which is probably for the best because the answer is always the same: nothing much happened, they just grew up and the show ended.
