November to March is the high season in Thailand and the best time to visit. Christmas and New Year’s is a busy time and according to the Lonely Planet, tourism increases by 50% at this time of year, especially on the beaches. If you are thinking of travelling to Thailand with a baby this is the best time of year to go as temperatures are more comfortable however you would need to book well in advance and be prepared for higher prices. Low season is from July to October where the monsoon season can cause heavy downpours and flooding. From March to May temperatures can get very hot and this is not a good time to travel there with a baby or a toddler. Northern Thailand is cooler all year round than the lower lying beach areas. It still gets extremely hot there from April to June and if you are bringing a baby during this time it is important to take extra precautions to guard against the heat.