Looking at VAF1B it clearly states in Section 7 Travellers under the age of 18. However when I look here https://www.gov.uk/family-visit-visa/eligibility Section 2 Eligibility: You must prove that you: are 18 or over.

I assume that the VAF1B is correct.

Interesting that Thai Visa thinks that travellers is spelt incorrectly.

Different rules apply to children, and children under 18 are not eligible for a family or general visit visa etc., instead they apply for a child visit visa.

In the days of paper forms a child visitor would use the appropriate VAF1 form depending on their circumstances; e.g. VAF1A if they were a child general visitor, VAF1B if they were visiting family.

However, in most countries, including Thailand, UK visa applications now have to be made online so the paper forms are largely redundant.

I don't understand your final sentence.

Yes I appreciate it will be done on line but just want to run through it on a paper copy first. I am concerned that the Thai person "helping" with the application is applying for tourist visa.

Just saying that when I type "traveler" here on Thai Visa it tells me that I spelt it incorrectly. Not so I think.

Since the abolition of the right of appeal for family visit visa refusals there is actually no real difference between a general, or tourist, visa application and a family visit one.

Who will be completing the online form; you, this helper or someone else? If worried, you can complete and submit the online form, then this helper can print out the hard copy to submit with the supporting documents when the child attends VFS to have their biometrics taken.

This is what I did for my sister in law's application in February.

If the form is completed correctly, then the application will be submitted under the correct category.

My understanding is that traveler is the US spelling, traveller the UK one. As far as I am aware, TV does not have a built in spell check; so if the spelling you are using is being corrected it is most likely being done by your computer's own spell check.