Research usually looks at adults first then children. If you have found no research on this for adults (cannabutter for toothpain), definitely don't give to a baby!
I'm inclined to Kizka's stance. Don't give mmj to a baby. I use cannabis from a script from my doctor. I would not give any of my adult prescriptions to my children. Under federal law, you're considering giving a schedule I drug (w no federally identified medical purpose), to a baby. Federally, heroin is schedule II. According to federal law, you've asked something worse than "my baby's teething should I run some heroin on his gums?"
Don't think that was your attention but this inquiry gives pothead parents a bad wrap.