At that height, this child sounds like the age of a Little Leaguer and an average length bat would be in the 29-31 inch range. However, the weight of the bat will also come into play when it comes to one that the child will be comfortable using. Bats come designated with a 'drop' ... this is the length of the bat, in inches, subtracted from the weight of the bat, in ounces. All youth bats are a minus 'drop', for example, a 30 inch long bat that weighs 25 ounces is a 'drop' of -5. Generally, the younger the player the higher the minus drop should be when it comes to the child being comfortable swinging the bat.
The -12 is the 'drop' of the bat and means the number of ounces the bat weighs is 12 less than the number of inches the bat is in length. If you have a 32 inch bat, a -12 drop means the bat weighs 20 ounces. If you have a 30 inch bat, a -12 drop means the bat weighs 18 ounces. If you know the length of the bat in inches and the drop, you can figure out how many ounces the bat weighs.
The general rule is to hand a bat to the child have him hold the bat at the knob, horizontal, at arms length. If the child can hold the bat steady without struggling for 10 seconds, then that bat is not too heavy for the child. But also make sure that the bat is not overly light as well. Try to get the heaviest bat that the child can handle.
Its however tall you are, the length of a bat doesnt matter its what fits you the best like if you were 5-6ft tall you would probably want a 31 inch or a 32 inch bat.
That number (-3, -5) is called the bat 'weight drop' and is the difference in ounces of bat weight versus inches in bat length. For example, a 33 inch long bat that weighs 30 ounces is a -3. A 33 inch bat that weighs 28 ounces is a -5. A 34 inch bat that weighs 27 ounces is a -7.
The biggest bat in Arkansas is the Hoary bat. It can be up to 5.9 inches in length, and have up to a 16.1 inch wingspan.
The typical length of the bat for a twelve year old depends on the weight and height of that particular child. My eleven year old hits well with a 28 inch bat and 20 ounces in weight. He is not quite 5 feet tall. So it varies on the child. Each bat has certain specifications and it also depends on the barrel. The one my son has is a 2 1/4 inch barrel. They also have ages on them. This one is for the ages between 7 and 12. So if your child is tall and has fairly long arms then you are going to want him to have about a 30 inch bat and weighing about 24 inches. But again, this varies with each child, get one that he feels comfortable with and doesn't feels like he is going to struggle to get a hit with it. If he feels comfortable with it the probability is better. So there is no typical bat for a 12 year old just make sure they feel comfortable and it meets your leagues criteria for baseball.