If you are planning to do a trek to Dudhsagar falls, it takes 6 hours to cover the whole area. There are other ways too but be what the trek is minimum of three hours and maximum of six hours. Since it’s a water prone area, swimming is allowed, but waters are deep so you have to decide accordingly. There are jeep safaris, where you get to see lot of wild animals. Dudhsagar Devi temple, Tambdi surla temple have lovely architecture which are safe to visit with a child. You could enjoy the Railway tunnel and track walk, again it’s a long walk so depends on what you decide.