Generic method to traverses Entity Framework parent child relationships

I am trying to write a generic method in a base class in my Entity Framework repository which will mark a record and related child records as deleted. Essentially to same function as EF cascade delete but updating a property on each record as opposed to deleting it.

In models my I have a Boolean property called "Deleted" as well as various navigation properties of type ICollection. I have created the generic method in my base repository called MarkDeleted which takes a single entity as a generic type parameter.

My plan is to iterate through all the properties of the entity and if it is the "Deleted" property set it to "true" and if it is a collection property iterate through all the entities of the collection calling the same MarkDeleted method passing the current entity as parameter.

I have got as far as setting the Deleted flag and Identifying which of the properties of the entity are collection properties by looking as posts such as How would I know if a property is a generic collection

My problem is to retrieve the collection of related entities from the collection property.

    public int MarkDeleted(T entity)
    {
        foreach (var prop in entity.GetType().GetProperties())
        {
            if (prop.Name == "Deleted")
            {
                prop.SetValue(entity, true);
            }

            if (prop.PropertyType.IsGenericType && 
                typeof(ICollection<>).IsAssignableFrom(prop.PropertyType.GetGenericTypeDefinition()))
            {
                foreach (var child in prop.xxxx ) //This is where I come unstuck. 
                                                  //How do I convert current property to its collection?
                {
                    MarkDeleted(child);
                }
            }
        }
        return SaveChanges();
    }

If I inspect this entity parameter at run-time I can see that EF has eager loaded all the related collections in the entity. So they are there I just need to figure out how to access them.