Costa rica - caribbean coast - Punta uva/Cocles/Manzanillo December

Hello, has anyone been to the Costa rican Caribbean coast in mid December? Our dates are 12 to 21 December and we are travelling with children (7 and 11 yo).

We were thinking of spending this portion of our (longer) trip on the Caribbean coast, thin crowds, nice wildlife, just a quiet relax. But we still want nice beach time and we just realised it might not happen in December due to weather. Has anyone any insight how does the weather and beaches in the area look in December? Or is it considerably better between 2 to 10 January (our alternative dates)?

And do you have comparison between Cocles vs punta uva vs manzanillo beaches?

Thank you so much for any recommendation and advice.