In December, the northern part of the Earth (where the teddy bears live) is tilted away from the Sun, and this means that we get the least hours of sunshine - giving us long nights and the shortest day of the year. It's when we have our Winter.
By March though, the Earth has moved further around the Sun, and now the tilt means that the Sun is facing right at the middle of the Earth. The rays of the sun are shining on the northern and southern parts of the Earth equally. This means we get about the same number of hours of daytime and night-time.
We call this time of year Spring, and the day of the year when we have the most equal day and night is called the Vernal Equinox. Equinox comes from the Latin words for 'equal' (aequus) and 'night' (nox) because the day and night were thought to be equal in all parts of the world on this day.