What to feed an old apple tree?

[Mum2020]

My parent's house has an old apple tree in the garden. Its from the 1930s i think. Still lovely, gives a lot of fruit every year. Does it need any fertilizers? Although it looks healthy and fine, every now and then we think - may be we should feed it something? My parents have 3 cats and they have grandkids over all the time. Can fertilizers be harmful to pets and small children? Is it best to leave it alone?

We just want the tree to be happy and healthy and have a long life :)

Do many of the windfalls rot beneath it? That should be enough.
The main thing is to ruthlessly prune it back each year. We e just done ours. If it has a good yield I wouldn’t want to inter fear too much though.

They pick up windfalls to minimise damage to the lawn. Because my parents are getting old now, they leave it to rot a bit before they can pick them up. Once in 2 weeks may be.
I don’t think they EVER pruned it though