I have made a t-shirt for my grandson with a picture of him made in cyanotype.
And now there is an important question, could it be toxic or harmful for my grandson to use the shirt?
Absolutely not. Prussian Blue is totally harmless... It's used orally for heavy metal poisoning.
Prussian Blue is also responsible for the color of blue jeans.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
~Antoine de Saint-Exupery
Having survived being liberally painted with Prussian Blue, as part of a Navy "Blue Nose" initiation for crossing the arctic circle, I can attest that there are no ill effects.
Stains for days yes, illness no.
Seems like first time you washed it, it would be ruined, imo.
You can liberate hydrogen cyanide from Prussian blue...but the chemicals you'd need to do so would be more dangerous to him than the cyanide itself