Nobody can tell you whether jelly fish are active or not, depends on several factors, and time of year is not one of them.
Can tell you though that there are no nets, plus can also tell you that there are no dangerous jellyfish on the Phuket westcoast beaches.
stevenl is right...At worst the jellyfish will give you a horrible urge to scratch....
The urge to scratch is strong....Try to avoid scratching,it will only make the itch worse....
I have surfed Kata heaps and rarely have I seen one....however,this was in low season when waves abound...Tho',I have brushed by a couple surfing in Khao Lak and they did make me itchy especially on the tender parts...Inside thighs,arms and neck...
There is a rumour that the box jellyfish is active in Thailand's waters but this,I reckon is just that...A rumour...!!...
Checking now about the net, normally there is, Katathani puts it up every high season.
No net but lots of people swimming.
Thank you so much for your reply. You have put my at ease. I was getting so nervous especially since we are taking our small kids to Thailand for the first time.
Thank you all for your replies. I had come across some articles online and started getting really worried. I'm nervous enough about taking my small kids on this trip ;-)
"There is a rumour that the box jellyfish is active in Thailand's waters but this,I reckon is just that...A rumour...!!..."
There have been a few sightings, but these are not on the popular westcoast beaches of Phuket.
We stayed at the Katathani and there was no jelly fish but I think it depends on the tides and the weather in any case as the others have said the Katathani will put up a net if they are around.
I don't think you should let the jellyfish situation worry you too much as there are beautiful swimming pools within the hotel complex that suit both adults & children far better than swimming at the beach.
Whether or not there happen to be jellyfish while you are there, you will find the water unsuitable for a 2 & 5 year old beyond knee deep as it can get quite rough.You can easily play with them on the sand & be only a few steps from the pools.
The garden & pool areas are excellent & I am sure you will have a wonderful time with your children.
"you will find the water unsuitable for a 2 & 5 year old beyond knee deep as it can get quite rough."
In December in general the water will be very calm.