Trekking means walking in an unspoilt natural environment. Eveywhere around here you can find short paths that fit families with kids: you can visit medieval villages, parks and nature reserves. Longer trips to the mountain pastures or the mountain huts are also available, but may require some extra effort. The closest routes are the Via Spluga and Via Bregaglia (in Valchiavenna, just a 30 minutes drive) and are quite easy to undertake. A more challenging one is Sentiero Roma in Valmasino, where some experience is suggested.
Looking for something more complete? Try Nordic Walking!