Some things never happen, some always do, and most are in between. Spin, roll and pick to see how likely each one is, then try it 100 times.
Taking out a yellow ball
Pick the word that fits best.
Impossible
It can never happen.
Unlikely
It happens less than half the time.
Even chance
It happens half the time.
Likely
It happens more than half the time.
Certain
It will always happen.
Chance = the ways it can happen, out of all the ways.
Start with words on a line from impossible to certain: impossible, unlikely, even chance, likely, certain. Spinners, dice and bags of coloured balls make it something they can see and count.
Count the ways it can happen and put that on top, then count all the ways and put that underneath. Rolling a 6 on a dice is 1/6; rolling an even number is 3/6, which is the same as 1/2.
Chance tells you what to expect on average, not what will happen each time. Toss a coin 100 times and you'll get about 50 heads, maybe 46 or 54. The more times you try, the closer it usually gets.
Children use words like likely and impossible at about 7 to 9, compare chances and write them as fractions at about 10 to 12, and run experiments to compare with what they expected at about 11 to 13.