Use Baby Soap or body wash to clean-up these areas.
Post giving the bath to baby , wipe out all the water with a firm cloth.
Many a time we leave these areas Wet ,which may cause infection.
Use power/body lotion for better skin there(there might be rashes due to Diaper use).
During normal weather, wash hair within interval 2-3 days.you can do hair wash daily if your kid enjoys it.