Together in Motion is a new playplace located in Arlington on the Somerville line.  There is a schedule of activities for both children (0-6) and adults.  Tumbling classes are offered to toddlers and exercise classes are available for adults to participate during morning and night.  There is also an open play time where you pay $7 (or $5 if under your baby is under one) for you and your child to play on the tumbling equipment; making tunnels, houses, mazes- you name it.  If your child is older, he or she can play alone while parents sit in the lounge reading or surfing the web!  Private parties are also available.