penalty after amending

Trying to decide if it's worth amending my 2019 returns to remove my 2 dependent children so they qualify for educational tax credits. I filed 3 separate 1040s for 2019--amending would result in additional refund amounts of about $1400 and $500 for the 2 children respectively. However, I would have additional federal tax due of $260. How do I calculate the late fees/interest that I would also get hit with?