Madhavaram Botanical Garden is one of Chennai's larger green spaces, laid out with sections for fruit trees, medicinal plants, indoor plants, cacti, and ornamental trees. It is a good change of pace from the traffic-heavy centre and gives families room to walk without needing to leave the city.
The garden is in north Chennai, so it makes most sense if you are already in that part of town or want a quiet outdoor stop rather than a major monument.