You did the right thing. He is a sick man. Whether it was accidental or on purpose, whether he was grooming your kids or just trying to get at you with "look what you're missing Pippi" (with npd that's a real possibility) or just trying to stir up a crapstorm, IT WAS WRONG.
And feel free to get angry, but all the people defending him and saying she overreacted remind me of my own parents sweeping my sexual abuse under the rug. Covering for their own terrible parenting, hoping I never said anything to anyone because it would expose their alcoholism, drug abuse, mental illness and basic parental negligence.
Minor children should not be exposed to sexual imagery of this nature. This is way different than accidentally finding dad's Playboys or watching Real Sex on Cinemax after everyone else is in bed.
If he was blackout drunk and forgot the photos were in the device, he is unfit to be around minor children unsupervised. If he knew the photos were on the device, he is a sexual deviant and unfit to be around minor children unsupervised.
Good job Pippi. Nolite te bastardes carborundorum. He is coming apart. You are getting stronger every day. And to answer your question, never send the kids with him unless it is court ordered.