I forgot to mention that the doctor wanted to test his speech development (at that age, he should have some words that are understandable without translation), so the doctor took a book out of Grandson_5's hand. GS5 loudly exclaimed "No! Mine!" The doctor said his speech is completely normal.

(Another comparison: Grandson_4, when the doctor was checking him for the size of his vocabulary, said "Well, actually I already do this". Both mother and doctor laughed. Grandson_5, during a similar test, was asked about his interests, and told the doctor about cirro-stratus clouds. I think they're all somewhat above those guidelines, partly because we read several books to them each day, including some books that delve into specific subjects like weather, space, and various kinds of animals. For example, the 3 and 5 year olds both use the words "carnivore" and "predator" when talking about animals.)