I know it well, walked along there many a time.
Forte Sao Joao beach is down (and back up) a flight of steps from anywhere up above it - there are some very des.res around there.
80 metres sounds about right but there is a low sandstone cliff hence steps and/or path.
You can walk along the beach, a very pleasant walk, into the centre of old town Albufeira in about 15 - 20 minutes. In summer the tides are not high enough to block that route. The beaches are wide and sandy with lifeguards on duty 11am to 7pm usually. At one end of that particular beach is a right-angled cliff and you do have to watch out for semi-submerged rocks. There are steps, then a path over the cliff, for exploring and at low tide rockpools and the like where the kids can search for creatures. The beach shelves fairly gently, so there's no sudden deep water but as always when the tide is high there can be some unexpected currents up near the cliff end.
There are beach bars/restaurants etc down that end as well.
Late May/early June the air temperature will be in the 70's easily; last May we hit 87F on a couple of days so that should make the water quite OK. There were people swimming etc in the sea yesterday if that's anything to go by.
Enjoy your trip.