Just a heads up for people with children who are applying for an extension...my husband and I just got our extensions yesterday but we brought our baby with us. The officials tell you that you do in fact need to extend for everyone, including babies. I'm assuming from what I've read on here, that it is technically required, although many people just don't do it because there is no fine up until about 14 years old. We didn't do it for our baby but may go back and do it, if it will cause problems down the line. Is it truly OK not to get baby an extension and then come back next year? If anyone is attempting this, I suggest not bringing the baby or child with you.
TLDR : Answer Summary
Parents applying for a visa extension in Thailand are advised that technically, extensions are required for all family members, including infants. Although there are no fines or restrictions for overstaying for children, their passports may receive an overstay stamp, which could complicate future schooling options in Thailand. Some immigration officers may overlook this requirement, suggesting parents don't worry about it. However, obtaining the extension provides peace of mind and complies with the law.