A children’s illustration is not meant to be a realistic depiction of an event, it’s to explain a concept. In this case, that a Jew and a Mitzri could drink from the same cup, one getting water and the other blood.
I once saw a picture (in a book published by a certain large Chassidus) for parshas korach, with Moshe and Aharon wearing streimels and korach had a bend down hat. Now why would they have had streimels if it was during the week, and if it was Shabbos, nobody could’ve taken the photo anyway. It couldn’t have been motzei Shabbos because it would’ve been dark and flashes weren’t invented yet.