Hi Nani!
Welcome in the germanspeaking Namibia forum.
Now we are becoming to an international forum...!
In May is winter, so there will be no mosquito bothering you and your kid.
You do not need additional vaccinations.
Any water coming out of tabs is very good, no harm with food and you will get your Yoghurt in Gababis in the Supermarket.
You will get one of the world best Beef Meat in Namibia, especilally Gobabisdistrict is a cattle country.
What are you doing there for 3 months??
If you got more questions to ask, you are most welcome!!