The first time that you realise that your child is a little bit sweaty can certainly be a surprise especially if they are nowhere near their teens.
It seems that the onset of puberty is a lot earlier than it used to be and tweens are needing to use deodorant a lot younger than their parents. Along with encouraging good cleanliness and hygiene the use of a deodorant will go a long way in dealing with sweat.
A deodorant as opposed to an anti-perspirant allows the body to retain it's natural function of sweating (which is the body's way to detox) whilst helping to neutralise body odour caused by bacteria breaking down sweat into acids on the skin.