Can we archive child records along with parent records?

Yes you can archive child records along with the parent record.

What is DataArchiva?

DataArchiva is a 100% Native Salesforce data archiving solution available in the AppExchange which can periodically archive your historical Salesforce data. With Auto-scheduler, Custom Archiving, Encryption, Integrity & Restore features, DataArchiva saves 85%+ storage costs, improves CRM performance & drives better governance.