Usually soap & water, but another thing that I've found works on the rare occasion I can't get them out with a simple soak is hairspray. It's great for all types of ink. Nothing special -- just cheap drugstore brand hairspray. I spray it on, let it set for a bit & if I can I gently hand agitate before tossing it back in the wash.
But I would try it on a small inconspicuous spot first with them being your mother's blocks. I've never tried it on anything more than 20 years old, or so precious a memory.