As an ITV production, the series is a staple on BritBox . While BritBox is largely English-focused, regional versions of the app on Apple TV or Amazon Channels sometimes provide local subtitles.
Use VLC Media Player or MPC-HC, which automatically detect and load subtitle files in the same folder. Little Boy Blue subtitles Portuguese (BR)
A vast database for finding rare or specific regional subtitles like Brazilian Portuguese. As an ITV production, the series is a staple on BritBox