I'm sorry for your loss. The IP PIN (Identity Protection PIN) is a six-digit number and is different from the 5-digit e-filing PIN. The IP PIN changes every year and the IRS mails the new PIN each year in late December or early January, to the mailing address on the last return that was filed with the IRS.
If your child passed in 2017 and those who handled the final arraignments (usually the funeral home) have done their job and notified the Social Security Administration of their passing, then the IRS has locked their SSN so that it can't be used fraudulently. That means even with the IP PIN the e-filed return will be rejected with an error code of "SSN LOCKED". So you will have to print, sign and mail the return to the IRS anyway. Non-receipt of an IP PIN by the end of January is a good indication the IRS has been notified of their passing. So if you do not receive an IP PIN for that dependent you have no choice but to print, sign and mail it to the IRS.
If there is a refund due on that dependent's return, then you might also need to include in your mailing the IRS Form 1310 which you can get at https://www.irs.gov/pub/irs-pdf/f1310.pdf. Read the instructions for that form to help you determine if the 1310 is necessary in your case, and what additional documents you may need to include with the mailed return.