yep.
Well worth it.
Particularly if your kid has deep crevices in their molars. It protects the actual surface of the tooth (even deep down in those crevices) from cavities, by preventing anything from actually being on the tooth surface (except the sealant itself)... so when your child doesn't do a thorough job cleaning those deep crevices every.single.time.they.brush---or even when they forget to brush---come on... they're kids now.... no sugars are left there to encourage bacterial growth and then cavities.
A word of caution though: don't let your kid eat/chew ice after the sealant is applied (a common, but bad, habit). It will cause the sealant to break and come off.