Normally, newly registered web2.0s are now considered as a new site, and the search engine may not consider its primary domain's authority, in which it may not flow down to its subdomain in that aspect. There are a few good web2.0 that are considered as good by the search engine, judging by the amount of web security that they enforce on their site.
If the web2.0s are not getting indexed, then you can either submit it to an indexing service - through a software or via those paid services, those can get the links indexed within a day - depending on which service. But such services may not stick - 2 months down the road, it may not be indexed any longer.
The only sticking way to make those web2.0s indexed is to further build links and tier it further with more backlinks, and it will have a longer lasting effect and link juice will flow accordingly through the structure.