Yarn for "hot" countries

Silk yarn might be a good idea. Silk is harvested and worn a lot in places like SE Asia, and would make lovely baby clothes (try Colourmart for supplies). Woollen yarns are likely to suffer from the humidity.

You could try Merino wool as this is good for all temperatures. My nz family use merino clothing all year round and dil knits lots of children’s things with it.

Bamboo yarn is very light, nice to knit with and very soft to wear.

Thank you all for the suggestions. I have ordered some bamboo and some merino to see how they work out.

I'd love silk but it would probably need to be hand washed.

There are some lovely fine merinos about as suggested.
How lovely to be knitting for little ones.

I live in a hot country and you would be surprised how cold we feel in our winter because you kind of adjust to the heat. Anything below 17c feels cold so I wouldn’t worry too much about ordinary wool.