Bolting a swing to the ceiling

I am trying to work out how to best tackle this job: installing a baby swing that hooks onto eye bolts mounted in the ceiling.

The swing/bolts needs to hold 20kg max weight.

I don't think I can bolt it to the existing ceiling structure as the ceiling trimmers are 70x35mm and the ceiling joists 90x45mm, spacing 600mm. The eye bolts are 8mm so I don't think you can drill that big a hole into something only 35mm wide, plus I would be worried I was decreasing it's structural capacity.

Would it be sufficient to buy a piece of 4x4 timber 90x90mm, then place it between two joists, screw the sides of it in with say 4 batten screws on each side, then drill the 8mm holes through the 4x4 and bolt the eye bolts to that?

I don't want to do overkill but I also don't want it to fall from the ceiling! Does everyone think this is the best way to do it?


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