Here's a really good explanation:
Yes, there is a possessive ‘s, but it is not like English.
For words that end in consonants other than s, there will be no apostrophe for the possessive, just add an s.
This word is simply plural: http://www.dutchgrammar.com/en/?n=NounsAndArticles.10
Yes, Dutch does have a possessive "s", but as spelling rules differ, compared to English it's less often written with an apostrophe:
A possessive apostrophe s is added to a noun or name ending in a vowel. "papa's jas" (dad's coat)
A possessive s is added to a noun or name ending in a consonant other than s. "vaders jas" (father's coat)
A possessive apostrophe is added to a noun or name already ending in an s. "Dries' jas" (Dries's coat)