wrstlmom1970, mmeditz
NFHS rule 4-1-1 deals with the rules regarding singlets. In essence it states that a singlet may be cut no lower in the front or back than the level of the armpits. And cut under the arms(the side of the wrestler) may be cut no lower than 1/2 the distance between the armpit and the belt line.
HOWEVER ... USAWKS Rules Modifications (which superceed NFHS rules) 4-1-1 states that "The legality of the uniform will be up to the referee, and need not conform to the NFHSA rule." The way I interpret this is that the head official of a tournament can make a determination as to whether these types of singlets are allowed or not. I would assume if it became an issue that official would ask the tournament director if he wanted to allow them or not. Personally I prefer that wrestlers at kids tournament conform as closely to the NFHS rules as possible. However because this kids modification exist there is the possibility that you will see a kid wrestling who is not wearing the "traditional" type of singlet. I have seen at some novice tournaments this year where a kid is wearing tight fitting shorts and a t-shirt.
The main thing the official should be concerned about is the safety of both wrestlers. Are these freestyle type singlets any more dangerous than the tradition one piece? Well I can't say for certain scientifically, but the fact that they are used in freestyle and internationally suggests that they don't pose any more significant risk than their counterpart.
So in conclusion the simple answer to your question is... Yes these singlets CAN be legal at kids tournaments, but that doesn't mean they will be in every case. It would be in your best interest if you are considering wearing one to bring both types with you to a tournament and speak with the head official and the tournament director as to whether you can wear them that day or not. They will make a determination at that time and you will have to go with that decision. Hope this clears that up.