I am a long time sewer and have recently decided to start my own clothing line for kids. I am making my own patterns but don't know how to decide on the fabrics. Does anyone have suggestions?

I would think it would depend on things like play clothes or not, summer or winter, if they are pants or a summer dress or a shirt and so forth.

Look at the drawing or whatever you have for each thing and picture it in your mind exactly how you think it would look best.
Go to the fabric store and visualize how you would use different fabrics that you particularly like