What is the ruling on experiencing arousal and an erection upon looking at or touching one's children, or thinking of them sexually, knowing that this occurs involuntarily and is accompanied by a feeling of distress and a desire to get rid of it? And is this considered a form of waswas (whispers/obsessive thoughts)?

The man should continue psychological treatment, persist in the remembrance of Allah, seek protection from Satan, and frequently say: "I seek refuge in Allah from the accursed Satan." Looking with lust is forbidden for anything other than one's wife, and touching is even more severely prohibited. Scholars have unanimously agreed on the prohibition of looking at a non-mahram woman or mahram relatives with lust. Looking with lust is absolutely forbidden for anyone looked at, whether mahram or non-mahram, other than one's wife or slave-woman. If a man feels lust when kissing a young girl, then he is not permitted to do so. Homosexuality has stages: enjoying a forbidden gaze, playful interaction and familiarity and embracing, and committing the major indecency. Persisting in the minor forms of these actions elevates them to major sins.