Cove (in Spanish Cala) Anguilla is located in Porto Cristo Novo and is easily accessible by both foot and by car. The beach area is roughly 40meters wide and 80 meters deep, hence plenty of room even on busy days.
There are beach lounge chairs under Tikki umbrellas available on a per-day rental basis (ca. 8 Euros/chair), however there is also plenty of room to spread out a few towels and an umbrella.
The water here is typically crystal clear and kids can walk in a few meters before it getting too deep. When looking out towards the water, on the right-hand side, you'll find cliffs which are semi-walkable where older kids and teens jump off (height ca. 3-5 meters). Further up this cliff there is a pathway. The Cala is also accessible here by foot, from the stairs leading down Passeig Infanta Carlota.
On the other side, the cliffs, further out are nice to snorkel and lead around towards Cala Mendia, which is swimmable. The markings to how far out you may swim allow you to go around towards each Cala.
Back on the beach, if you forgot to bring something to eat, you'll find a Cafeteria with a few lunch options and snacks like french fries, olives and the such, along with cold drinks and ice creams for a reasonable price.
If you plan to arrive by car, then you will make your way towards Passeig Alfonso XII, a narrow street with cars typically parked on both sides and traffic heading in both directions, however, easily maneuverable, all the way to the end where there is a roundabout. The way towards the parking area of Cala Anguilla is off to the side, not very visible. Carefully head down this street (again two-way traffic), until you get to the bottom where there is plenty of free parking. The beach is easily accessible by foot, only a few meters away.
Overall a nice Cala to visit with children.