In this case drawing a closed way with *[highway=pedestrian][1]* with and *area=yes* seems fine to me. If bicycles are allowed then add *bicycle=yes*, too.
Alternatively there is a [*area:highway* proposal] [2] which suggests to use the tag *area:highway=footway* without(!) an additional *highway* tag. This isn't currently rendered anywhere as far as I know.
Note that you can always specify the [width][3] of a way, although it won't get rendered at the standard layers at the moment.
[1]: http://wiki.openstreetmap.org/wiki/Tag:highway%3Dpedestrian
[2]: https://wiki.openstreetmap.org/wiki/Proposed_features/area:highway
[3]: http://wiki.openstreetmap.org/wiki/Key:width