Kids don't need body wash but body wash is a good cleanser for kids.
Kids can use bar soap for cleaning their body's when bathing or showering but body wash is better for kids and even adults at getting clean.
I personally myself use bar soap first and then use body wash after so I get double clean but it doesn't really matter what you use for yourself or your kid for keeping clean.
Whatever is cheaper or better for yourself or your kids to use will will fine.
Many kids use bar soap for washing their body's as do many adults.
However some kids and adults prefer body wash.
Make sure your kid gets their private areas clean and also their armpits as sometimes some kids tend to miss cleaning those areas.
Aveeno daily body wash is good for kids and teens and adults.
Although kids can use adults or other body wash but for kid's it's best to use body wash that is formulated for sensitive skin.