i need tips on how to juggle kids

i have a extremely needy 3 week old baby. seriously all day she wants to be held.. then i have an extremely needy 5 year old.... so needy that she wont do ANYTHING alone including play.. so if I'm sitting on the couch tending to the baby ALL DAY so will my 5 year old.. its blazing hot where I live lately so going outside (with a newborn) isn't really an option... i need tips on how to keep my 5 year old active. I'm worried her being so inactive will in turn make her overweight. please no rude comments, just a mom looking for advice