Having a single letter incorrect in your children's last name may or may not cause your return to be rejected due to a mismatch between what was filed and the data that the IRS compares to.

If your return does reject due to the misspelled name, just correct it and resubmit your return.

If your return does not reject and has been accepted by the IRS, just be sure to correct the information next year when your tax return data is imported automatically.  You do not need to file an amended return to correct the spelling for 2018.