In a caption of the photo, Gosselin wrote, "I'm sorry...but where has this little guy gone? My 4 year old little professor is all grown up! Talk about 'edible'! I adore his sweet, kind, loving, sensitive self! And he's so thoughtful and helpful! OH-and his love of HIS dog, Mak, especially melts my heart every single day!"
Her followers took issue with Gosselin focusing only on Aaden and fired back, with one follower writing, "Too bad she'll never do that [throwback photo] with Collin. She's GLAD he's gone."
"WHERE IS YOUR 'OTHER' SON, COLLIN THOMAS GOSSELIN?? HMMM? YOU ARE SUCH A LOSER PARENT," another user wrote, before adding that they felt the same way about her ex-husband Jon.
The concern for Collin comes from the fact that a little over a year ago Gosselin announced that the 13-year-old was going to be going away to a facility to deal with "special needs."
Earlier this year, however, Gosselin reportedly revealed that Colin was "flourishing," and added, "He's responding very well to one-on-one instruction. He definitely finds it easier to function and cope better without all the chaos that his home life entails."