We used to have a flag league here for kids 8-14 (at 15 the are allowed to play tackle).
One team had a lot of kids and decided to split into 2 team, one of 8-10 and one of 11-14.
Almost all of the other teams had most kids at 12-14 with 1 or 2 young ones, who got in at some point to keep them interested in the game, but played vey little.
All the games against the 'all-youth' team were blowouts, and I was R for the game at the end of the season where they got an interception, and scored a touchdown (2 firsts!)
There is NO WAY I was going to throw a flag when they and the coach all ran into the EZ to hug the RB. Even most of the opponents had a smile on their face to see these little guys so happy!
That coach was great. Always complementing his players, complementing the oppenents, asking questions about the game. Generally just trying to get his young charges interested and invloved, and make sure they didn't feel bad about always loosing.

I would guess that describing a "chest bump" to 100 officials would paint at least 75 different pictures. As with almost any behavior on a football field, the degree or intensity of the contact has a lot to do with deciding whether, or not, a "talking to" or a flag is the appropriate reaction.

Other factors that usually impact that decision are the game situation, the tone and temperment of the contest, and in a situation like a "chest bump" the spontinaety of the act itself.

The bottom line is that sometimes a chest bump may go over, "the line" and sometimes not. The idea that all such acts are the same and should be treated alike, just like so many other actions in a football game, is nonsense.