Are there ... children in the park? (many, much, a)

Are there many children in the park? - Есть много детей в парке?

Many - (много) is used with countable nouns.

Much - (много) is used with uncountable nouns.

A - is indefinite article. Indefinite article is not used with plural nouns.

There are many books in the bookcase.

There is much water in the cup.

There is a book on the table.

There are many animals on the farm.

She drinks much coffee.

There is a pear on the plate.

He has got many lessons today.

He has much time to do his lessons.

He has a lesson today.