My first child

If you think you already have enough diapers to get you through potty training, it is obvious it is your first child. LOL Buy your diapers as needed or go with a diaper service.

Two reasons not to stock up on diapers;
1. have to use all these diapers, so no reason to rush potty training. Don't want the kid starting school in diapers though.
2. As others said, each kid grows at his own pace. The smartest mathematician in the world couldn't calculate how many of each size diaper you will need.