Don't these two sentences mean the same thing?

Question

"Nous avons DAVANTAGE d'enfants que lui" and "Nous avons PLUS D'enfants que lui"

I put 'davantage' and it was marked wrong.

Answer

Bonsoir Aleida,
According to the Collins-Robert:
davantage de and plus de have the same meaning --> more.  
I am uncertain the reason that «plus de» is more commonly used in this type of syntax, perhaps it is better for the pronunciation linguistic effect.

Bonne chance et bonne continuation

Answer

Hi Aleida, according to my understanding "davantage" and "plus" are synonyms. It is just that davantage is more formal. And you can't use it in comparisons where you would use plus as in "I have more apples than you" -- "J'ai plus de pommes que toi." You could not use davantage in this example.

-- Chris (not a native speaker).