Solved
[ROM] Child Spellcasters Can't Summon Familiars
Product: The Sims 4 Platform:PC Which language are you playing the game in? Svenska How often does the bug occur? Every time (100%) What is your current game version number? 1.107.151.1020 DX9 W...
Never mind. Apparently they just need a lot of room to summon familiars, and I happened to try it in several too small spaces. I'll leave this report here, in case anyone else runs into this problem and looks for a solution.
