I teach third position before second position, because it is easier to find third position from first position. (Place 3 on A in 1st position, slide 1 to same position to arrive in 3rd position). It also maintains a visual when sight reading that is easier to understand, lined notes on 1st and 3rd fingers. It also allows the palm of the left hand to rest or touch the body of the violin in third position, so it’s like a ‘marker’ that you can feel you are in the right place. So if you can’t hear it yet, you can feel it.
Second position can be introduced if you have pieces or exercises to reinforce it. You can make the point that first finger moves up a step and there you are in 2nd position, although most players are a little overwhelmed with no ‘tactile’ anchor and the reading music shift (1 and 3 playing on space notes). Are you using a step by step violin repertoire? If so, let this be your guide. I use the Suzuki violin material. Third position is introduced and reinforced from Book 2 or 3 and up. Second position isn’t introduced until about Book 4 I think.