C.K.
I'd recommend getting the crowns, particularly if they are his molars, which the permanent teeth won't come in until around age 9 or 10. My daughter already lost one molar due to a large cavity because we tried to go with just the filing option, and eventually the tooth broke and we had to have it pulled. Now she has this big space holder in her mouth - which is kind of like a retainer - so the other teeth don't shift in and take over the space where the permanent molar will come in. We got the other molar where she had a cavity crowned after that.
Good luck.