in all honesty, i'd take DD2 with you - it's less stressful on everyone. if you're BF, you'll have to build a supply (which is hard to do at such a young age when still getting BF sorted), you'll have to pump while you're away (and probably dump - such a waste!) and it might impact your supply. DD2 will be free to travel with to a fair degree - i'd take her along.