No. Knowing the ABC’s in order isn’t important until a child learns alphabetical order.
What is important is for a beginning reader to hear and say the 42 sounds of English, and to be able to associate each of those sounds with a letter or pair of letters.
Some reading specialists recommend not showing a child letters until the child can repeat the sounds. In English, sounds come first. Sounds are paired with one or more symbols (letters) so we can show sounds visually.
When I teach children sound-letter pairings, I start with the consonants since most consonants, like “b” and “k,” are always pronounced the same. Then I move on to short vowel sounds, saving “e” and “i” until “a,” “o.” and “u” are learned since “e” and “i” sound similar. That still leaves more than a dozen sounds to match with letters or letter groups.
However, many teachers drill the ABC’s by singing the ABC song. They might test beginning readers on the order of the ABC’s, making allowances for the “L, M. N, O” section which is almost always the last part learned.
Find out what your child’s teacher expects. But to answer your question, no, knowing the order of the ABC’s is not important for beginning readers.