What are the financial requirements for a DTV application in Thailand for a family with children?

We applied through british emabassy and our kids did not need to prove the 0 bht

Also, for the kids, you don’t just add them on. You submit seperate applications (with the application fee) along with the documents required (proof of relationship to initial DTV holder, initial DTV, financial proof, etc.).

500k per applicant for London so 2 million baht.

For the DTV, each applicant is assessed individually, including dependants. In practice this means that the financial requirement applies per DTV application, not per household, and children also require their own DTV if they are staying long term under this scheme, even if they are under 16. As a general rule, the 500,000 baht requirement therefore applies per applicant, including children, unless the specific embassy explicitly applies a different internal policy, and some embassies may accept the financial requirement for children to be satisfied through a financial guarantee as a sponsor letter issued by one or both parents, but this is not standardised and must be clarified directly with the relevant embassy or consulate before applying.

When I did it, I used the same 500thb for myself and 2 kids. In your case you'll need 500thb for each adult application, then when applying for dtv dependant, include the parents bank statement along with a sponsor letter