Exchanging Kenyan Driving Licence

Biggest challenge for you will be language. Everything in Poland is in Polish. Elder people don't speak English, so better to relay on younger ones. Good news is that after living in Kenya, you will find food, accommodation and everything else very cheap there. Shopping will be fun!
I think only cell phone service in Poland is more expensive than in Kenya, well perhaps bananas too. Other than that, you will find things cheap.
Hope you have a job there already. Unemployment these days is pretty high.
People in general are rather friendly, we like foreigners, but avoid young muscular men with short haircut. They are bored with their miserable lives, often unemployed so they spend their days drinking and looking for trouble. They might have some nonsense racist ideas.
Weather in Poland is not as warm as in Kenya. Right now, it should be getting warmer, it is a spring time, but I heard they are expecting snow storms. Summers are warm to hot, something like in Nairobi, but during the winter expect snow and temperatures might drop even to -25'C. Houses though have central heating.
We use metric system. No one will know what is an inch or foot or acre.
Don't drink water from the tap. It is not lethal but not recommended either. Boil it first or buy bottled water. There are no power cuts there and internet is fast and relatively cheap.
If you will be living in a big city, buses (no matatus there) can take you around. Its pretty convenient. Many Poles don't have a car. If you or your kids would need to commute with a bus, consider buying a ticket for 3 months (bilet sieciowy in Polish), as it is much cheaper than to validate new ticket for every ride.
Oh, and be very careful with taxis taken from the airports, especially Warsaw Airport. They will charge you double or triple. Bus 175 will take you with no hassle to the centre of Warsaw and main train station there.
As for driving license, before you leave Kenya, get international driving license in Nairobi. I think you don't need to obtain Polish one as long as international will be valid. Once you are in Poland you can find the office which issues driving licenses and ask what is the procedure. Unfortunately I don't remember exactly the name of an office and the procedure. Plus, it might be different for Poles and different for Expats. It takes week or two and wasn't expensive.