The quinoa grain is naturally coated with a sustance called saponin. It is very bitter and "soapy" tasting.
Quinoa is usually washed to remove most of the saponin before it is sold in America. However, some quinoa is washed more than others. I've had quinoa that really didn't need rinsing, and I've had quinoa that had a horrible bitter taste when I forgot to rinse.
I almost always rinse mine no matter what, as I can really taste the difference even in quinoa that has been pre-rinsed relatively well before being sold.
If you made the quinoa for your son and it did not taste "off" or bitter than it is just fine.