"I’m just a grandma trying to get great pictures of my grandson! "
Well grandma I don't believe there is any age restriction in photography. I am a grandpa (9 times over waiting on the greats) and I do the same. However, unfortunately, there is a stature or endurance issue. And unfortunately, more powerful telephoto lenses are big and heavy not to mention expensive.
I am going to assume you have tried the 75-300mm and I am assuming you have to shoot from the stands or bleachers. Two issues here. That is not a good place to be for shooting from. Secondly 300mm, your long end, is probably not long enough to give you that tight up close shot. Unfortunately, using that word a lot aren't I, the answer to either isn't easy. You need a longer, more focal length, lens and/or you need to be on the field.
Although there is another possible solution, get DPP4 from Canon. It is free so no reason not to get it. It is a photo editor that will allow you to crop your images. It may be possible to use the gear you have now and simply crop in post editing. It will take a little bit of learning to use DPP4 but lots of folks do and I see no reason why you can't. There are lots of videos and tutorials on the ole inner web to show you how. You can do as little, like cropping which is very simple, or as deep, total editing, as you like.
If you feel a bigger tele lens is the solution the very best is the Tamron SP 150-600mm f/5-6.3 Di VC USD G2. (Model A022). I would strongly suggest you try one before you buy it because of the mention above about big and heavy and expensive.
DPP4 is free! 😁
EB
EOS 1DX and many lenses.
