Even if the little boy is technically just your shapeshifting girlfriend who she morphs into, it still feels so weird to make out with him/her. So why can't you stop yourself? Your hands cores hid tiny body, so small and fragile. You then carry pin the "boy"(who is your transformed girlfriend) to your room and put him on the bed, his slender arms unable to resist the strength of one of your hands while the other goes wherever you want. S/He can't stop you (not that he wants you to stop) because it feels so good. S/He moaned in seeming confused pleasure with your tongue throughly exploring his/her mouth. His hairless legs curled around your waist. A strand of saliva lingered as you lips parted from his panting mouth. His adorable face was flushed red and his eyes gazed half lidded up at you. "How was it?" you break the silence.
"Teehee,... it's a bit weird and too sensitive with this little body, but I'll get use to it." your shapeshifting girlfriend in 10-year-old boy's form answers and breathes.
"If you say so, babe. Besides, you're very cute in this body, even if you're a boy." you smiles as you still pinning the little boy's arms above his head, you go to nipple on his right nipple while your free hand plays with his left. To your surprise, your girlfriend/brat reacted far more to the nipple play than the tickling. Wow, is he really that sensitive?
"Ah! Ah! Aaah! That feels...! Oh! Mmm... Oooh. Easy there, please, slow down... Aah!" You do not slow down though. Nibbling, pinching, licking, flicking, circling, sucking... You play the moaning boy like an instrument, until his quivering pleading becomes incomprehensible babble.
Sticking your fingers into his mouth and making his suckle on them, you use her/his saliva as lube as you begin to finger him, opening his hole one finger at a time. Now you were just far too turned on to second guess yourself.
Now he's finally ready. You let go of his pinned arms and use both hands to grip his hips. She or he's no longer trying to hold back, but just twitching and drooling as if you've already broken his mind.
A twinge of awareness returns to his eyes as the tip of your lubed up cock finds the brats quivering hole. "Honey..." the boy whimpers, half in fear, half in need. You shove into him and he throws his head back and moans. One long passionate moan as you slowly push deeper and deeper and deeper into your transformed girlfriend.
Finally all the way in, you look down at the gasping little boy beneath you. You can't believe how tiny his body in cimpated to yours. Yet you're inside him. Her? You don't care anymore. You pound away, holding the little boy by the hips and thrusting as fast as you can. He cries out, clutching the bedding like a life raft. He's so tight as the bed rocks as if on a turbulent sea.
You raise his hips so his knees are next to his head and your pounding him directly down into the bed from above.
"H... honey!" your girlfriend / boy cries out after ten minutes of relentless fucking. "I think I'm about to... come...!" Sweat dripping from your chin, you pick up even more pace and time you orgasms to sink up. You fill the brats ass as he let's out a stream of cum all over his own face.
Panting, you lie down next to you girlfriend and watch his cum covered face. You could get used to your girlfriend looking like this. After the orgasm, you decided to take the tissues and clean your girlfriend/little boy's face and body from his cum. While you finish cleaning him/her up, you both give each other a kiss on the lips. "So, what do you think?" your shapeshifting girlfriend/boy asks.
"It was strange and weird, but I think it's great." You reply. "And no matter who you turned into, I still love you, babe."
"I love you too." you both then continue the kiss as you make out with him or her. Later, s/he breaks the kiss and asks. "So, what shall we do next?"