<c:ChildCreatorComponent obj="{
                                    sobjectType : 'Contact',
                                    LastName : 'Rossi',
                                    FirstName : 'Mario'
                                }" />

<c:ChildCreatorComponent obj="{
                                    sobjectType : 'Contact',
                                    AccountId : MY_DYNAMIC_ID,
                                    LastName : 'Rossi',
                                    FirstName : 'Mario'
                                }" />

<c:ChildCreatorComponent obj="{
                                        sobjectType : 'Contact',
                                        AccountId : {!v.recordId},
                                        LastName : 'Rossi',
                                        FirstName : 'Mario'
                                    }" />