ABC is known as the three basic letters that were introduced from childhood. In the alphabetical order of letters, A then B and then C letters are the earliest sequence. It would be better for children to learn the alphabet from the earliest sequence. This method also makes it easier so that when using many methods to learn ABC does not become random because on average all methods of learning words begin with ABC letters.
To learn more from ABC letters you must pay extra attention to the child. Keep in mind, that preschoolers are classes for children to play with the given lesson elements. If you give lots of letters, it can have an unpleasant learning effect for children because they feel they are more dominated by learning activities than playing. But for some smart kids, they will show signs that they can learn more from ABC letters in preschoolers. To those children, maybe you can give extra letters aside from ABC.
In a class, of course, the character of each child is different. You cannot make a child understand ABC’s letters at the same time. In one case, there was a child who couldn't write ABC letters properly. But not being able to write might be too harsh for him. Because what he really needs is a more active practice in writing. Children who are trained to write will be better than children who rarely practice writing. So it is not an impossible thing for children to write ABC letters well. An exception can be made if your child has special needs making it difficult to write ABC letters well.
Struggling is common in the learning process. If you surrender, surely you will not get satisfactory results right? Both for teachers or parents and also children, if you are struggling in the alphabet learning process, all will produce good results if all parties do not give up. Parents and teachers have an important role to give extra attention to children. You can use many methods when teaching alphabets to children. If it doesn't work using the workbook method, you can use playing or listen to songs. There are so many ways to be able to help the child rather than having to give up.