I have one for you. It's an oldie, but fits your request:
Dean, Tell Me A Story (http://www.fanfiction.net/s/3346173/1/Dean_Tell_Me_A_Story)
Sammy just wouldn't go to sleep...

I want to start out saying, is that I love this fic. It has major overprotective Dean, and a sick Adult!Sam being treated like he's about five. It's adorable and really fluffy. I've read it several times, and after I post this I'm going to read it again; that's how much I love it.

That being said, this isn't wee!Sam. He's an adult, and he just got his soul back. It's not exactly what you're looking for, but it's still worth the read in every way.

Pause by vail_kagami
http://ficviendha.livejournal.com/97795.html
Summery; Sam has his soul back and gets sick. It's not that bad, no matter what Dean seems to think. Overprotective!Dean and somewhat grouchy!Sam.

Prompt;Sometime after getting his soul back, Sam falls ill. It's nothing life threatening, but he feels pretty miserable and can't really get out of bed - though he does try. Sam plays it down, but Dean won't have that. Ever since Sam's soul is back and Dean knows it's only a matter of time until the wall breaks and he loses his brother again, Dean is even more overprotective than in his best days, and now Sam's sick, he is in full "Take you medicine!"/"If you get up one more time I'll tie you to the bed!"/"Shut up and let me read you a bedtime story!" big brother mode.

Just saw this and fell I need to make this correction. This fic wasn't written by me but by the very awesome minviendha. I just made the prompt it's based on.