Just 150 minutes away on the French side of the border, you'll find Font Romeu. A charming little village dating back to the Roman era, a popular ski resort in the winter months and the gateway to hiking the lakes at Bouillouses from June to October.
To the north of the ski resort, you'll find lac bouillouses and a hostal (les bones hores) for accommodation, drinks and snacks.
There are a few ways to get to lac bouillouses, all of them require a little effort which is no bad thing as it keeps the crowds down, but by far the easiest (and most panoramic) way is to take the chairlift from the free car park at La Calme (€19 all day family pack - 2020 prices) and then an easy 30 minute hike along the valley to the hostal.
From the hostal at lac bouillouses, you have a variety of stunnungly beautiful and relatively easy hikes. The boucle des étangs takes you climbing towards Pic Carlit (2921 mts / 9583 ft) and 13 lakes mostly above the treeline.
The les étangs des esquits takes you through the forest and to four beautiful lakes: estany de la pradella, estany negre, estany llarg and estany del racó.
The third walk is a variation of the boucle du lac d'aude which continues to another valley called les camporells and the estany de la basseta, estany del mig and estany gros. This walk is easy, albeit 10-12km, and there is a refuge at les camporells where you can get refreshments and basic accommodation at prior notice. You can also access les camporells via the ski resort of formigueres and a 3hr climbing hike. If you really want peace and solitude, les camporells is your place as it is too far for the average day tripper. Wild camping is allowed throughout this area from 19.00 to 09.00.
The first two of these hikes can be done in a day and with children from 4-5 years old and babies in a back-pack. We took our two daughters (4 and 20 months). The hike to les camporells and back is approximately 20-24km or so and with children, you should plan to camp or take accommodation at the refuge. As always, safety comes first and in the high mountains you should take the bare minimum of survival equipment (just in case) and plan your hike with a solid weather forecast.