I see more selfishness in both of them and nothing childish about Mbappe. If a player wants to show his prowess on the field or his abilities when competing with other teams, I think that's very reasonable, but if it's more of the selfishness of the two of them, it means that they both need additional advice after the game.
In fact, if the two of them can cooperate with each other in a healthy manner, then whatever the team and the two of them want to achieve, I'm sure it will be realized.
I don't know if you remember it, but behavior like this was generated when Neymar joined PSG and collided with Cavani, and this generated some tension in the whole team, for me Neymar is the one who makes these things happen, and it wasn't I blow here, I remember that when he played for Barcelona, he always tried to take away or collect Messi's free kicks, of course Messi wouldn't let him, but it was annoying and funny how he insisted on doing what he wanted, sometimes I see that Neymar It's like those children who want to do everything and shine only he, this makes some players take some dislike for him, even though Mbappé is now the one who has more fame.
Neymar and Mbappe both want to be the best at PSG, sometimes tensions arise between these two players because of each other's selfishness. But speaking of selfishness, Mbappe is even more selfish than Neymar. This can be seen from the comparison of the number of assists recorded by Neymar and Mbappe during five seasons with PSG. Neymar has provided more assists than Mbappe.
Mbappe feud with Neymar could add to the crisis in the PSG squad. Christophe Galtier must unite their two attackers in order to work together to get positive results, he must make the (MNM) trio of Messi, Neymar and Mbappe more productive in scoring goals and assists for PSG victory. Moreover, PSG is struggling to get the UCL title for the first time, harmony between players must be created to achieve the goal.