Fans love Shipping. Fans love cute kids. And sometimes the most popular couple in the show will end up being composed of two of the cute kids. This results in the occasionally squicky practice of Shipping two characters who are barely old enough to be in a relationship (but in fairness this isn't as squicky as pairing them off with adults).
A Toy Ship does not automatically qualify as squick since usually people only support innocent childhood crushes between the two; most writers and fanfic authors go with relationships that are along the lines of just hugging and declarations of love, or they let the characters age up in canon before anything.
For In-Universe examples of kid couples, see Puppy Love. Not to be confused with Cargo Ship, which is about shipping people with things like toys.
