This is an excellent example of why it's a good idea to only take travel advice from people who've actually been to the place in question
Will you just shut the f*ck up Harry.
You're like a broken record. I have been to Poland many times, my wife is from Gdynia. If you keep spreading lies about me then I will start with you........
Message to the mods-if you want to ban me then do it but idiots like Harry who carry their poison from thread to thread get away with it. I replied in all helpfulness to the OP. I haven't baited Harry yet he can't stop being a d*ckhead.
Lisa, sorry for that but this forum has it's fair share of bullies who try to dominate threads by belittling the opinion of other members.
Now, as you are going to Gdansk in December I thought it was pointless in telling you that the "winter is cold" blah blah blah. I assume you know all of this anyway :)
I wasn't suggesting you don your bikini but children love beaches whether it's hot or cold and I still maintain Sopot and Gdynia have nice beaches that your child will enjoy. Yes, it will be cold but you'll be dressed warmly. There's a famous pier in Sopot that on fine days, (even winter days.....Harry) people promenade up and down taking in the view whilst kids love feeding the swans on the beach (took me a while to get used to seeing swans on a beach-here in the UK you only get them in lakes and rivers).
There is usually a skating rink just at the front of Sopot pier in December which may or not be your thing :) Kids especially love the chocolate bars, Sopot has one called Blikle or Wedel (always get them mixed up) where they serve an amazing array of hot and cold chocolate drinks....google it !
Gdynia also has a nice beach with it's own kids playground right on the sand. Polish winters can be harsh but Poles are used to it so if you're blessed with a sunny day in December then there will still be plenty of people walking around.
There is also an aquarium on the pier in Gdynia which kids love.