"Losing" is part of both the game and life, the kids will get over it. I mean, as kids we played games like TMNT and Battle Toads and we managed, not getting 50 coins because you got kicked out of the gym is nothing on comparison.
But yea, if you want to be extra nice, you can look out for these things and lose all your PvP battles.
Honestly, if you care about kids' experience that much, join them in raids, that does much more.