writing down what we do so that might help bring some context.
A new engineer joining a team will usually be on hunt for information regarding how everything works. Quiet a lot of these information needs can be met by a good Employee handbook (we pin posts/lists in #welcome on slack). Add a friendly HR person who helps him with cultural aspects and PM who gives a big picture view of what the team is doing and what it is trying to achieve and you are 80% there.
Having learnt the lessons hard way , for me the biggest problem in on-boarding an engineer to a team is that it slows down the team drastically. At-least for two to three weeks and current engineers usually hate it.
So a better way to go about it is to make him contribute to the project in however small way as soon as possible. we do this by making him/her ship a small bug fix or feature enhancement to production within their first week usually with the help of just one existing team member.
There is a risk in depending only on one engineer to onboard new members. He will get bored, he might have some bad practices which will be picked by the newbies et al. So we usually do these one-week exercises with 3 different people during the first 3 weeks. After that the newbie becomes a contributing member of the team and every team has it’s own dynamics regarding how people grow within.
Applying your thoughts on Sidekicks to this we have a HR sidekick + Product Sidekick (who is usually the product manager) +A solo sidekick for each of the three weeks culminating in the new engineer pushing one feature/bugfix a week to production.