- so you're looking at a non-0 (Guardian) visa for which, presuming your child is attending full-time school in Thailand (I believe) you need to show a min' bank balance 500k บ plus paperwork from the school verifying enrollment/ attendance.
Roger - to register the house for TM30 I uploaded the house owners Thai ID card and house tabien baan (blue book) - you'll need a Thai reader just to help navigate the registration website. Once registered - immigration email a login name and password after 2-3 days, after that its relatively simple to add "foreigners " to the houses tm30 record.
Worth noting there is no print function from the online TM30 page so take a screenshot of the record to print later.
If you can register your house for online TM30 - you'll probably need a Thai reader to help to register but once done relatively simple to update after each trip abroad - no more 100km trips.