There appears to be some confusion and I would like to correct that.
Firstly, no. Unders 13s cannot see social links. 13+ users can say “Twitter”, “YouTube”, “Twitch”, using the filter. “Discord”, no. See this help page and Section 1, rule 13, bullet point 6 of the Community Rules, this DevForum annoucement/reminder and the images below.
On top of that, they can say the URLs as well
Discordapp.com may be an unintended bypass and has been formally reported
This is quite a good idea but would be risky, it could be seen as asking for PII (Personally Identifiable Information) which violates the Community Rules (See section 2, rule 1, bullet point 5 of the community rules). You may find it better to shoutout a phase like “Follow {username} on Social media”, or just simply “Follow {username} on Roblox”. If they’re over 13, they can see their social media there.
Depending on how the filter is for under 13s. you may be able to go a bit more direct and let the filter handle it