H's sister had it when she was about 8 (so quite a bit older, but I'm guessing the same principle applies?) and she had literally 10 spots, randomly dispersed over her body.
Unluckily for me, I'd not had the pox before, so at the grand old age of 18, I caught it off her. I was covered. We're talking 1p sized boils
all over my body, in my mouth, down my throat, soles of feet....everywhere, without even a square mm of free space. And I got shingles with it.
So, in answer to your question, yes, you can get it mildly. Although I'm not saying thats what your LO has. x