I hate seeing thoughts. MC's or other characters.
Some of it has to do with the fact that humans have a lot more complex thought process than just "Oh look, my son is sleeping naked, oh what a huge cock!". Now I immediately think that character is an airhead moron.
Other parts of it have to do with the fact the authors are shit at narration. You can explain a scene in text without giving us 'thoughts' at all. Let the reader parse out the thoughts.
Example of narration vs thought dump.
Thought : "Oh wow, my son has such a huge cock, who knew? Now I want it in me! Am I a terrible mother?"
Narration: Diane slowly crept into the room, nearly tripping on all the junk on the floor. She looked around for safe places to walk, tip toeing barefoot through the room, but the room is dark, so she moves slowly and deliberately. A soft sigh escapes her lips as she steps on something soft. Thankfully, its her son's shirt, and not a dirty cum rag. Next to the shirt, she finally spots what she has been looking for - his backpack. She slowly unzips the bag, reaches in, and pulls out the letter she asked him to retrieve from the mailbox. She breathes a sigh of relief upon checking the mail, finds it unopened. She clutches the letter in her left hand, and starts to look up from the backpack, when suddenly her son shifts position in his bed.
Diane sighs again, as she realizes he's still sleeping, but pauses when she realizes his shift in position has revealed the fact that he's been sleeping naked. She pauses, her heart racing now. Small bits of perspiration run down her cheek, as she finally makes up her mind. She reaches out to adjust the blanket to cover her naked son, and reveals a rather large cock, semi hard, now fully revealed for her to see. Its still dark, but she can judge the size of it. A small gasp of surprise escapes her mouth, which she quickly stifles by biting her lip. Despite the room being slightly cold, Diane is very warm now, and alarmed at her own response to her flesh and blood's semi-erect manhood, she drops the blanked back where it was, turns around, and starts walking back out of the room.
She pauses halfway to the door, however, lets out another sigh, and tip toes back to her son's bed, to lift up the blanket for another look, this time, not only taking in the sight of his cock, but his slender frame, his soft belly, the hair growing on his chest, his young but handsome face. She sets the blanket down again, composes herself, and tiptoes slowly out of the room, this time, not stopping halfway, but making it to the door, slowly opening it, and exiting the room.
Her heart is racing as she steps out into the hallway, her body warm and on high alert. She slowly, quietly, closes the door, and pauses for a few moments to catch her breath, wiping the perspiration off of her face with the sleeve of her pajama top. Her body is shaking and shivering, and it takes her another minute to finally compose herself enough to walk down the hallway to her own room, barely aware she's still clutching the important piece of mail in her left hand.
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Same conflict of emotions, but no need to brutally beat the reader/game player over the head that the mom might be down for some sexual escalation with her son. Let the reader decide/decrypt what the mom might be thinking, and allow your game to continue to build from there.