Chopta is the best place for a family vacation. it's a great choice. The highest Shiva temple Tungnath Trek is approx 4 km which may take approx 2 hours to cover. Since you are with family (kids) consider an extra half an hour.
I suggest to consider climb 1 km more to reach Chandrashilla, it's the peak of the mountain and the trek is easy and worth climbing because you get to see a 360 view of the Himalayas.
Also, there are a couple of tea stalls on the way so no need to worry about anything. I would suggest trying burash juice, it's a red flower of Uttarakhand. it's good for our health.
Have a nice trip and pls don't use plastic, don't throw any garbage on the mountains. Happy journey :)