
Suppose you have stored accounts in lstAccount variable then in VF you can do like this :
<apex:pageBlock id="pb">
<apex:repeat value="{!lstAccount}" var="objAcc">
<table border="1" width="95%">
<tr>
<td>
<h5>{!objAcc.Name}</h5>
</td>
</tr>
<tr>
<td>
Proveedores <br/>
<table border="1" style="margin-left:10px;" width="90%">
<apex:repeat value="{!objAcc.Proveedores__r}" var="objProv" rendered="{!objAcc.Proveedores__r.size > 0}">
<tr>
<td><apex:outputField value="{!objProv.Proveedores__c}"/></td>
</tr>
</apex:repeat>
<tr style="display:{!IF(objAcc.Proveedores__r.size == 0,'block','none')}">
<td><h1>No Proveedores</h1></td>
</tr>
</table>
</td>
</tr>
<tr>
<td>
Opportunities <br/>
<table border="1" style="margin-left:10px;" width="90%">
<apex:repeat value="{!objAcc.Opportunities}" var="objOpp" rendered="{!objAcc.Opportunities.size > 0}">
<tr>
<td><apex:outputField value="{!objOpp.Name}"/></td>
</tr>
</apex:repeat>
<tr style="display:{!IF(objAcc.Opportunities.size == 0,'block','none')}">
<td><h1>No Opportunities</h1></td>
</tr>
</table>
</td>
</tr>
</table>
<br/>
</apex:repeat>
</apex:pageBlock>