[SalesForce] How to get Cases, Opportunities, Contacts Associated with Account Object Dynamically

I need to get all the associated Contacts,Opportunities and Cases, for a given Account, if there are any.

Right now, I am doing something like below:

public List<Case> getCases(SObject sobj){
    List<Case> casesList = [SELECT (SELECT Id,Status,CaseNumber FROM Cases) FROM Account WHERE Id=:(String)sobj.get('Id')].Cases;
    return casesList;
}

public List<Case> getContacts(SObject sobj){
    List<Contact> contactsList = [SELECT Id,(SELECT Id,Name FROM Contacts) FROM Account WHERE Id=:(String)sobj.get('Id')].Contacts;
    return contactsList;
}

public List<Case> getOpportunities(SObject sobj){
    List<Opportunity> opportunitiesList = [SELECT Id,(SELECT Id,Name FROM Opportunities) FROM Account WHERE Id=:(String)sobj.get('Id')].Opportunities;
    return opportunitiesList;
}

Is there any better and efficient way to achieve this using dynamic apex??

Can somebody give directions on how to tackle this?

I am guessing this can be simplified alot using dynamic apex but I am not sure on where to start.. Any clues??