Measure from the inside edge of the beam (where it steps up to the ceiling height) back 1-1/4" and you should hit the middle of the first 2x12, or whatever they used to make up that beam.
Pre drill with a masonry bit, smaller than the threads of the lag bolt/ eye hook, and see if you hit wood above the hardi trim. If so, you can continue to predrill with a wood bit. It needs to be about or just bigger than the main shaft of the eye hook so the there is still wood for the threads of the hook to grab to.
Thread the eye hook in, hang on it a bit with your weight or something heavier than a toddler, 50-60 lbs, and if it holds, you should be more than good with two eyes hooks on a toddler swing.
This assumes they did a double 2x12 or similar header, you'll likely have a 1/2 gap between for the plywood spacer, unless they make their headers different with 2x4's top and bottom.
If you don't hit wood, the hole is small enough to caulk over.