One thing to be careful of - some items have restrictions on them. If your children's book is going to be sold, you can't use things from Rubio's Room for example. The terms of usage say, "Non-commercial use only." (If that has changed, please let me know. I've been drooling over the dress Carolly is talking about.) You will find this restriction on some of the free stuff around. As far as I know, anything you buy can be used for commmercial renders. (I know that's the case at Rendie, DAZ, and Poser Pros.) Many freebies can be used for commercial renders, but you have to read the readmes, site terms of usage, etc. Cheers!