Is Google mail safe to use?

Well it depends on what 'safe' means. If you mean safe from hackers and stolen personal information, then very safe. If you mean safe from children viewing inappropriate images, then not very safe. You can set up a safe-search setting, which only allows 'clean' images through the filter. However, this setting can be easily changed to allow inappropriate images to be viewed. So, it depends what 'safe' you are looking for.