Stu and Didi go on a cruise to Mexico for their fifth anniversary, so the Finsters are left to babysit Tommy. Tommy is pampered by Chas because he was playing alone and Charles thought that meant he was lonely. Tommy and Chuckie see a family tree and thought babies grew on trees, then, due to sharing some interest, Tommy and Chuckie decide they must be brothers. Meanwhile, Didi is vomiting due to nausea, which was revealed to be actually morning sickness as she was expecting Dil.
Home video releases
Rugrats: Season 5
This episode marked the first appearance of Chuckie's paternal grandparents (Chas's parents), Shirley and Marvin.
Marvin and Shirley are said to still be in their fifties, so they're significantly younger than the rest of the grandparents on the show. It can be assumed that they were probably somewhere in their twenties when they had Chas.
Like "The Santa Experience", the title card sequence is used twice in this episode -- once after the opening credits, where the title card says, "The Family Tree Part I", and again after the first commercial break, where it says "The Family Tree Part II". Also, the music in the second title card is different than the regular fanfare used in the first title.
Throughout their anniversary cruise vacation, Didi becomes very ill, with her and Stu assuming it's seasickness. Morning sickness (what Didi was experiencing), happens during the first trimester of pregnancy. This starts during the first couple of weeks, and ends after a month of being pregnant. Stu and Didi must have had conception within days, or less than a week of boarding the ship. This is very confusing and strange as to why they were unable to deduce this. Due to the fact that Stu and Didi already have a child, they should have already known how pregnancy works. Stu even confirms this in the final scene when Didi starts to become sick in the doctor's office, "We have to get used to this again". So the way this was set up seems very confusing,
One of Angelica's "bad" tactics is to have Chuckie spray water from a gardening hose onto Tommy. However, water is sprayed everywhere in the room that Tommy was in, and in that room was the computer that held the family tree, which somehow escapes the watery mess.
What Tommy, Chuckie, and Angelica don't know is they aren't and never will be brothers or sisters.
This is the last episode to use the 1991 Klasky-Csupo logo after the credits. From The Rugrats Movie onward, the 1998 Klasky-Csupo logo would be used after the credits.