I have this pushchair for my 2 1/2 DS and 12 week old DD. Obviously she's in the flat newborn position and he's perched above. The thing is, I'm not sure what to do next and when DD will be ready for the swap and to go in the small chair underneath. Making DS walk isn't an option as we often go out all day and he needs a rest / sometimes a nap and occasionally restraining. Any advice welcomed...