"De kinderen horen geen vogels."
Translation:The children do not hear birds.
"The children do not hear birds" - "De kinderen horen geen vogels" is correct. For example, if it would be: "The children do not hear the birds", it would be - "De kinderen horen de vogels niet". For your example: "The children do not see the birds" ("do" word should be here, not "does", because "children" word belongs to plural), it would be then - "De kinderen zien de vogels niet". We fit in "geen" with not specific, abstract things (for example, to any shoes, any birds) and "niet" with specific things (the shoes, the birds). "The" ("de"/"het") is a definite article, which shows, that we are talking about a specific thing, so we use "niet". "Zij eten het middageten niet" - "They are not eating the lunch" (they are not eating the lunch, that was cooked for them at restaurant, not one of any lunches, but stated, defined, that we know, about what lunch we mean exactly, about one, that was cooked at restaurant - "the lunch"). :)