There are a number or places that you can visit with your family and will have problem taking your kids especially. If you are fond of sea- Digha and Mandarmani. Then there is Sikkim and Darjeeling for the hills. Gorumara in Duars is also not a bad option.Plus there is the Sunderbans or Bakkhali. A visit to Mangroves can be quite educating for the children.
Every destination is kids friendly even Goa or Maldives for a fact.. now what does your little ones prefer? winter or summer .. better to chose accordingly.. for winter.. sikkim, Darjeeling .. and for warm places, Digha, Tajpur, even Bankura, Shantiniketan are quite an option