Let me first say , my response was more for the USA Petitioner . If the beneficiary has something I can't personal speak to that but technically JV crimes are not convictions for the purpose for immigration. if you read case law you can see several times where a person had admitted a JV crime at that point immigration / USCIS is allowed to request information since you disclosed this now you are considering this a conviction that's the way they see it and are able to justify it in the response to the appeals , but it's noted that JV offenses are not a conviction for immigration in the case law. If the record is sealed this is not a true expungement and if it's not expunged its best to disclose this in most cases it will show up depending on that state.
Also some states do not report JV convictions in the early years due to privacy. I know one state that personal told me they do not report to FBI . I also know a person that was 16 that had a AWA not aggravated , I spoke to and they were approved for the CR1 without a waiver or anything required. If they are charged as an adult or required to register forget it, then you for sure need a waiver or will be getting a RFE. If the person under 18 is required to register then that follow under the guidelines for the aggravated section under the AWA and will be disbarred regardless of the age. The state at that point must report the registration to the federal level which USCIS would be able to obtain even if expunged in most cases but not always.
What's funny is about 90% of attorney's are not properly trained with handling Juvenile offense regarding AW let alone information about JV crimes. There's hardly any case law on sponsor's applying for a beneficiary that had AWA convictions as a Juvenile. One of the biggest law firms in the USA that handles AWA cases is not even educated on Juvenile offenses. They will even tell you this and they handle the biggest amount of AWA cases . This also clearly shows you that uscis is not concerned about offense as a Juvenile to me since there is no case law on it or record of appeal. I would say anyone with a criminal history should just skip the k1 and do the cr1 it's less headache. You still must be honest with your spouse and let them know because there's always a chance that this could still come up in the interview if the record wasn't expunged correctly.