as in - my 7 month baby needs a quiet place to sleep for a good chunk of the day and then needs a quiet place to feed and then a clean floor to crawl around on... Whereas My 3 year old needs to be running around outside and meeting people and generally doing the opposite of the baby.
If I stay in for her naps and go out when she is awake then she gets no exercise. If I go out while she sleeps so my son can run about then she risks being woken up.
I hadn't realised it didn't get easier once the baby was bigger! I feel guilty about one or the other all the time at the moment!