How many businesses that are registered in the database can be attributed to 'Good for Kids'?
can be attributed to 'Good for Kids' refers to attribute_name = 'Good for Kids' and attribute_value = 'true'
SELECT COUNT(T2.business_id) FROM Attributes AS T1 INNER JOIN Business_Attributes AS T2 ON T1.attribute_id = T2.attribute_id WHERE T1.attribute_name = 'Good for Kids' AND T2.attribute_value = 'true'