Without a pop top or high top it would really need an awning for sleeping. It doesn't need to be huge! Depending on the ages of the children it is pretty easy to sort out who sleeps where. Two or three in the van, two or one in the awning.
We don't have a pop or high top but we do have a very useful small awning which could be used for sleeping but the larger awnings often have dedicated sleeping areas.
Or, just a tent that you can put alongside the van if you don't want to add an awning rail at this stage.