Finally,my son had the flu.

Finally,my son had caught the flu.
That's why he have has to be absent from nursery school while for five days.
I was disappointed because he was going to join a recital of nursery school this weekend.
I was indeed looking forward to seeing it.
I can't help it.
Fortunatly,somehow he is has no fever.
I was wondering if he really has the flu.
For your information he have has not been vaccinated.

But my second son doesn't hasn't get got the flu yet.
I hope the flu of elder son doesn't infect the second son.

Keep practicing! Your vocabulary is okay, your grammar just needs a little practice!
Your word order is really good though!  Good luck.