I've had all 5 of my children in t-ball over the years and in varying states and towns and leagues. 3 are in "modified t-ball" now, age 6.
You will find that leagues will vary. We had the same situation as you're experiencing now. It's ridiculous! We never understood why the older kids were put with the younger kids.
Some leagues vary on a starting age. Some start at age 4 and some at 5. If you're going to start with 4 year olds, then it should be age 4 and 5 for basic t-ball and age 6-7 for modified t-ball. (modified t-ball is where the first half of the season you use a T stand to hit from and the second half the coach slow pitches to you, most at age 6/7 are ready for that by 2nd half of season.)
In your situation, it should be age 4/5 for basic t-ball only, but some leagues throw them all together for multiple reasons which most make no sense.
Depending on the type of coach you get, some will pamper the older kids because they feel they need more attention as the little kids only need to know the very basics at such a young age. But this just proves that they should be split up.
Yes, it is very annoying, but you can't change the league. You can voice your opinion and expect to have equal treatment of players.
As for the balls, all t-ballers use a real, hard baseball, nothing softer about them. Not heard of that. Those softer balls are things you can use at home but I've never seen nor heard of that in regular league play.
I would teach him as much as you can on your own. Part of the game is learning the basics and one of the first things you learn is fielding and that is learning to stop the ball and not let it get past you, even if you have to use your body. Also, learning to use two hands when fielding. Teach him to put his other hand top of the glove so when he tries to field a ball it doesn't roll up to his face. The free hand will stop it from rolling up and keep it in the glove or on the ground so he can grab it. Ask the coaches a lot of questions to teach him at home.
It's not right nor fair to have him playing with larger, more experienced kids. I always hated that! But if it's the only league in the area it'll be something he'll have to work around. I always thought it would be better to split those ages up and only have a few teams each and play each other multiple times rather than have more teams as it's not fair to the little kids who are being pushed aside and not fair to the older kids who are at an age where they need more guidance.
Let him play but practice a lot at home and ask for tips on safety and be more involved during practices. Voice your opinions to the league commissioner and don't allow yourself to be brushed aside as a worrying caregiver.
K. B
mom to 5 including triplets