Rain cover for bike with attached child seat?

[rumtumtugger]

I have just bought a bike, huzzah! And a rear-mounted child seat to ferry dd around. I need to leave the bike stored outside so would like to find a waterproof cover for the bike that also fits over the child seat. Is there such a thing? Would I need to get a bike cover and a child seat cover like this separately? And if so, how would that all fit together??

Thanks

I think I'd just go for a tarpaulin/big piece of plastic, plus a few clothes pegs to clip it on in strategic places.

Yep that's pretty much what I've done! Thanks.