This is actually the best training for tinies.
They won’t hold long on battle with giants. So she is teaching them to satisfied a giant or a giantess so they spare them. And a training with feet work with other parts too. A giantess might want to use him as toilet paper in the woods or want him to tickle her feet.
And with male giants, who are more difficult to please than goddesses, he will have to lick his balls or cock if he want to survive.