How many {child} are to/by {Jean le Rond D'Alembert} ?
Jean le Rond D'alembert has how many children?
How many children do Jean le Rond D'Alembert have?
SELECT ( COUNT ( ?q ) AS ?a ) { ?q property:child resource:Jean_le_Rond_d'Alembert }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P40> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q153232 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P40 wd:Q153232 }
3