Is It Safe To Give My Child Uneven Halves Of Ciplar LA , Or Should We Use Ciplar Instead While He Is Also On Warfarin?

Doctor has prescribed half of Ciplar LA 20 mg for my 10-year-old son. We have started the tablet since the last 3 days. We are currently giving this at night 9 pm since that time he is available with us. He is also on Warfarin at 6pm dosage of 4mg and 5mg. My questions: 1. While cutting a 20 mg LA the exact half is not achieved. some bit gets powdered. is it ok to give such parts which may be a 40% one day and 60% other 2. Since Ciplar LA 10 mg is not available at any chemist can we give Ciplar 10 instead of half of Ciplar 20mg? Kindly guide.