I will be making a teddy bear birthday cake and I wanted to make little t-shirts and shorts for them...
I am not really sure how to do them.
Any advice?
TIA

The only thing I can think of would be fondant, but you would have to piece the clothes on him and assemble them after he is baked and crumb-coated. Is he 3D?

If you don't want to do fondant, you could just do buttercream which may be easier. You could use the star tip or just ice it smooth and use the Viva on it.

Are you making a cake with bears on it or are you making a bear out of cake. did I explain this right? If it's a cake-bear i would do what Annie wrote about the buttercream. If you are making a cake with little bears on it I would do cut out fondant over already made bears

If he is 3D you will have to make a template of the shirt and short pieces in paper and then cut them in fondant, then crumbcoat and apply the pieces.

Williams Sonoma used to have a bear pan that came with templates, but I never got it.

They don't have it anymore, but it used to look like this.

http://www.kaboodle.com/reviews/build-a-bear-workshop-cake-pan-with-princess-soccer-outfits
http://www.kaboodle.com/reviews/build-a-bear-workshop-cake-pan-with-santa-outfit