Outdoor playset ground attachment tips

Hi, i am planning to build a playset like the pic I attached here. I will have a tower and bridge with monkey bars underneath. I am in doubt if i should bury the posts to the ground with concrete or if i can just build everything on the ground surface and then attach it to the ground using anchors? I see lots of playsets to buy and they seemed to be just attached with anchors.. my children are 4 and 2 years old, i think they will use it for a couple of years and when they are done, it needs to be removed. I want the playset to be secure for them to play, i dont want it falling or moving with storms...I will use 4x4 pressure threaded lumber posts. If bury them is the best option, is there any special requirements? or just dig the hole, place the post and pour concrete? I've been searching for projects and how tos to build playsets but this questions remains in my head. If someone could give me an insight on this, i would appreciate it.