I shouldn't use the word difficult - it's more that they've been really easy babies until now. I would spend about 20% of my day actively attending to them, and the rest cleaning, cooking, browsing the internet or watching TV while they played happily 
Obviously I didn't expect life to be like that for long, but now they need more stimulation I'm not really sure how to provide it? I do the same things as I have done before - read to them, sing to them, silly faces etc. But it doesn't take any extra time! Now they are starting to fuss very quickly and it's difficult to settle them back down. We do go for a long walk almost every day, and have done from the beginning. What else can I do with them?