O.D.
My 4 year old had a lot of cavities even though I did everything I could to avoid them. One day she got an infection and we went to the dentist. The dentist treated it and she did do a root canal treatment (it was not painful for her and it did not take long). I did not want to have the tooth out since she was only 4 and the new tooth ( a molar)takes a long time to come out. She did say that if the infection comes back, she will have to take it out. There was no crown since the dentist did not see the point of it.
After a month, the infection came back so we had to take the tooth out. Now she has a spacer to keep the space for the new tooth. So there are other options if you want. My kids' dentist is a pedriatic dentist. Maybe you should talk to one, too. Good luck!