They have mum and baby groups in the library and different kinds of sessions at Community Vision in Penge, eg, music and movement, baby makaton. Some you have to call and book. Also, Baby Sensory Beckenham does sensory sessions at Azelia Hall on Mondays and Tuesdays but you have to book online for those! We've been going to various ones for a few weeks and my boy is 4 months. We started getting out at 3 months - it was a good time to start being more sociable!
Baby yoga and baby massage at Beckenham Place Park. Nursery rhyme singalong at the library at Beckenham spa on Mondays at 10.30 and 11am. Free Sensory classes too local - Google Hartbeeps.com for loads more classes