1. Question: According to Rashi why can’t you teach your child to count the omer in the daytime if it is too late for them to say it by night?
A. The Mishna Berura (70:2:9) brings down the view of Rashi that there is no obligation on the father to teach his child to say krish Shema by night even at a chinuch age because he is not found by the father, since it’s too late and the child already went to sleep.
B. This makes sense for nighttime Shema which can only be said by night but the halacha is by the omer if you didn’t say it at night, you should say it without a blessing during the day and it counts so why not do that with your child?
Answer: Since that wasn’t way the mitzvah was ideally set up, to be done during the day then it is improper chinuch to teach it that way and the only proper way to teach it would be to teach him by night with the blessing which is impractical if he goes to sleep. (See Dirshu Mishna Berura volume 5 in back page 41 footnote 9)