For kids 9-12 months+, cut each grape in half. Cut each half in half, then dice. Aim for pieces about the size of 1-2 peas so the kids can pick them up but they are small enough to easily chew. (You do not need to peel the skin.)
For kids 12-24+ months, cut each grape in half vertically (or longways), then cut in half to make long quarters.
For kids 24-48 months, cut each grape in half vertically (or longways).
For kids over age 4, grapes may be served whole but always be sure the kids are sitting down to keep them as safe as possible.
Notes
Store cut up grapes in an airtight container in the fridge for up to 2 days.