can parent and child flow have different resource computation in prefect 2.0

yes, that's possible - we call it orchestrator pattern https://discourse.prefect.io/t/how-to-create-a-flow-run-from-deployment-orchestrator-pattern/803 in the future, this may get even easier than this, but I can tell any details yet, but you're gonna love it! Planned for release in the next few months