Remove the tank cover and check the water level after the fill valve has shut off. It should be about one inch below the opening of the overflow tube. If it is significantly lower than that, there may not be enough water in the tank to fill the bowl after a flush. Correct this by adjusting the float.
The average child can do this during the second half of this year. Between 24-36 months, children are typically able to work simple insert puzzles (e.g., completes a three-piece simple puzzle where pieces are whole objects). Also, children can remove a part from a toy (e.g., a wheel) and replace it.
The truth is, all children need help learning how to use their senses. From the very first day they are born, children are designed to explore the world via their senses. That's why babies and toddlers touch everything and put it in their mouths.