The book you're describing is likely The Inchworm and the Giants by William Pene du Bois, first published in 1959.

Key Matches:

• Three Kids: The story follows Tom, his sister Mary, and a friend (often mentioned as a companion in adventures) as they explore a magical world.
• Giant Inchworm: They encounter a magical inchworm named Walter, who can grow to enormous size. The children...

The Last of the Really Great Whangdoodles by Julie Andrews Edwards (1974).

Why it matches your memories:

• Three children travel with a professor into a whimsical but perilous fantasy land. The chief adversary they keep running up against there is the Prock (the Whangdoodle’s gatekeeper), which can come across as an “evil ruler/prince” figure in memory.
• There’s a set piece where the kids ride a...

This is almost certainly The Worms of Kukumlima by Daniel Pinkwater, published in 1981.

Let's check your memories against the book's plot:

• Timeframe: Published in 1981, it fits perfectly with a book you would have read as a child in the '80s.

• Protagonists: The main character is a young boy named Ronald, who travels with his eccentric uncle. They team up with an old adventure...

You’re thinking of

Knee-Deep in Thunder
by Sheila Moon (Macmillan, 1967; very widely re-issued by Scholastic in the 1970s-1980s).

Why it matches the points you remember

• Three children from different backgrounds are the protagonists.
– Maris (a girl from California),
– Hal (an English boy) and
– Raf (a boy whose father is from India)
are swept out of the ordinary world an...

You weren’t imagining it – I finally tracked it down. Thirty years ago it appeared under the rather obscure title

The Third Magic
by Welwyn Wilton Katz

(First published in Canada in 1988; U.S. paperback a year or two later.)

Here’s how the pieces fit your memory:

1. Three “modern” kids – Katz’s heroes are teens from our world (two North Americans and a third of South‐Asian ...

Identifying a Children's Fantasy Novel with Unique Elements

Based on your description, I believe you're looking for "Seven Spells to Sunday" by Andre Norton and Phyllis Miller, published in 1979.

This book features three young protagonists who travel to a fantasy land and contains some distinctive elements similar to what you've described. While I can't confirm with 100% certainty that thi...

The book you’re remembering is
“The Worms of Kukumlima” by Daniel Pinkwater (Dell / Yearling, 1981).

Why it matches the scenes you recall

1. Three child protagonists
   • Russell (the narrator, an American boy)
   • Osgood “Ozzie” Sigerson (Russell’s brilliant friend, whose father is an Indian diplomat – the “Indian” boy you remember)
   • Their class-mate Norman Bleistift (another Ameri...

<think> Hmm, the user is trying to identify a children's fantasy novel from the 70s or 80s. They remember three kids traveling to a fantasy land, with one possibly being from India and the others from the US or UK. There's an evil king or prince, and two very specific scenes: riding a giant inchworm where the middle rider gets stuck in a tunnel ceiling, and someone eating glowing mushrooms and bei...

Based on your description, I believe you're looking for "The Worm of Kukumlima" by Daniel Pinkwater (1981).

This matches several of your key details:

• It's a children's/young adult novel from the early 1980s
• Features children who travel to a fantasy land
• Has the distinctive giant worm that characters ride with saddles
• The middle rider bouncing up and down as the worm moves is a memorab...