Julie,
Your dream seems to weave together themes of protection, responsibility, and autonomy, which might reflect your waking life's emotions and situations. Beginning with the vision of being at home with your husband, a place of comfort is slightly altered, suggesting a sense of unfamiliarity within the familiar. Being with your husband's ex-wife's child can symbolize your role in your current family dynamics, possibly feeling the weight of responsibilities that aren't originally yours. The child's resistance to leave with his mother might mirror your own internal struggles with letting go or your protective instincts towards those in your care.
Transitioning to the driving scenario, the highway often represents life's journey with its direction and purpose. The incident of hitting something on the road and the subsequent accident into the water could represent unexpected challenges in life. You're facing a crisis, but you're also the rescuer, managing to save your family—this could point to your perceived role as the one who keeps everything together in tough times. The car not sinking and your ability to restart it and drive out of the water signifies resilience and the capability to recover from adversity.
Lastly, the visit to the repair shop where you are overcharged but then realize the repairs are unnecessary may symbolize your feelings about being taken advantage of or second-guessing decisions in your life. It could be an expression of your desire for greater control and understanding of when to assert yourself, especially regarding financial or practical matters.
Your emotions during these sequences, although not intensely negative, do suggest some underlying anxieties or concerns in your waking life. These dreams might be a manifestation of your subconscious working through feelings about your role in your family, your ability to cope with crises, and your independence in decision-making. Remember, these interpretations are based on common dream symbolism and your provided context, and only you can determine which elements resonate most with your personal experiences and feelings.