Oh you definately want to fill them. My daughter had 3 cavaties at age 3.... If I didn't fill them they would probaly be huge by now and rotting and painful. I'm not positive but I think the cavaties/infection stuff can pass on to the permanent teeth before they even come in.
My daughter is now 6 and thankfully hasn't had anymore. It has nothing to do with her brushing her teeth she does a good job at that she just has bad genetics. Her dad has horrible teeth and I donot and she's taking after her dad. Or it could be that she was on the bottle til 2.5 years old. Although at bedtime I only allowed water. But in the daytime she had juice and other things. And it's all her back teeth that were effected.
Because my daughter has such a problem mouth I have always taken her to a pediatric dentist. My insurance covers this so I take advantage of it. They are just more kid friendly etc.
You never know when your kid will loose her teeth that have the cavaties. My daughter is 6 and hasn't lost any teeth, and probaly will be more like 9 or 10 before she looses the specific teeth she has the fillings in.
I'm very pro-dentist, my parents were with me and I am with my daughter. I guess you just see kids that don't go like my next door neighbors and at 12 they're teeth are horrible and nasty and look more aged than most adults teeth.
If you don't have dental insurance or adequate insurance there are programs out there, like at the colleges and stuff that will do it for free or very low cost.
As far as getting it filled it was hard on me. I was almost balling watching my daughter flip out in the dentist chair. She has issues with the easy stuff at the dentist like flossing. They had her cavaties filled and done in 1/2 hour and thankfully we haven't had to do that again. Just regular check ups.