I can't help you in that I haven't ever owned them but I did have the opportunity to have a VZN 80 in my system for an extended period about 9-10 years ago, glorius indeed!
Your concerns are the same as mine and a reason I ultimately decided against them, I was considering the VZN 100's, too big, too much heat from the VZN 80 as it was and I was concerned that the amount of heat generated would most probably shorten the life of the parts and there would be frequent service issues. I can't comment further on this since I've never owned them. I have read on these forums by an OTL manufacturer that a reason his company ruled against using the 6C33 tube was the amount of heat generated at the plate and the resultant fatigue that would result to the sockets. In other words, sockets should be replaced with the tube. Don't know about that for sure but it would certainly be a concern, especially coming from someone familiar.
The bottom line is that there are tradeoffs for such a degree of magic the Joule provides and one has to ultimately decide whether it is worth it or not. I am sure if I had a dedicated listening space I would have seriously considered their purchase. It seems you have arrived at that point, especially with a toddler that has access which would be MY biggest concern. I hope it works out for you. There are other amps to consider, I have a Berning zh270 which I've owned for 10 years with not ONE issue including tube replacement and it is in regular use daily. It is no longer in production and I will say it doesn't have that harmonic envelope or the huge sound of the Joule. The two are quite different but IMHO the Berning is more natural to the source, OTL transparency, clarity, scale, speed and wonderful tonality. These amps have that uncanny ability to really separate instruments and voice in acoustic space which renders a realism to recorded music, as do all the OTLs I've listened to. The big deal with the ZOTL amps by Berning is that there is less heat and they are easier to place but they may not be your cup of tea. With a good source and well sorted out system they have a natural sound and presentation that I haven't heard bettered. Again taste would come into play and it might be too hard to walk away from the addictive sound of the Joule! You should at least listen to the newer zotl models if you haven't already. Different for sure but better, only you can decide.
Your concerns are the same as mine and a reason I ultimately decided against them, I was considering the VZN 100's, too big, too much heat from the VZN 80 as it was and I was concerned that the amount of heat generated would most probably shorten the life of the parts and there would be frequent service issues. I can't comment further on this since I've never owned them. I have read on these forums by an OTL manufacturer that a reason his company ruled against using the 6C33 tube was the amount of heat generated at the plate and the resultant fatigue that would result to the sockets. In other words, sockets should be replaced with the tube. Don't know about that for sure but it would certainly be a concern, especially coming from someone familiar.
The bottom line is that there are tradeoffs for such a degree of magic the Joule provides and one has to ultimately decide whether it is worth it or not. I am sure if I had a dedicated listening space I would have seriously considered their purchase. It seems you have arrived at that point, especially with a toddler that has access which would be MY biggest concern. I hope it works out for you. There are other amps to consider, I have a Berning zh270 which I've owned for 10 years with not ONE issue including tube replacement and it is in regular use daily. It is no longer in production and I will say it doesn't have that harmonic envelope or the huge sound of the Joule. The two are quite different but IMHO the Berning is more natural to the source, OTL transparency, clarity, scale, speed and wonderful tonality. These amps have that uncanny ability to really separate instruments and voice in acoustic space which renders a realism to recorded music, as do all the OTLs I've listened to. The big deal with the ZOTL amps by Berning is that there is less heat and they are easier to place but they may not be your cup of tea. With a good source and well sorted out system they have a natural sound and presentation that I haven't heard bettered. Again taste would come into play and it might be too hard to walk away from the addictive sound of the Joule! You should at least listen to the newer zotl models if you haven't already. Different for sure but better, only you can decide.