I love the balance that a parttime job provides. I feel very fortunate to have this option. It allows me to dip in and out of childcare and professional life, without getting burnt out in either world. The key is a truly flexible job (rather than one where you end up cramming 5 full days into whatever pt hours you work) and earning enough to pay for ft childcare and cleaning services.
Just had my appraisal at work and feeling very happy about this. I have always taken the full year off on maternity for both dcs and then gone back pt.
The difficulty with a stint of SAHM-dom is that unless it is fairly short (less than 2 years' max?) many jobs don't allow you to step off and step back on without a substantial discount when you try to get back on, especially on a pt basis. By keeping my foot in the employment market at all times, I have only taken a slight discount for moving to a flex role and pro-ration but still take home a very good wage, just a fraction below dh, though his career will continue to take off whilst mine has naturally stalled.
Also, I feel it very important to be able to support my family should my dh not be around for whatever reason. We won't be pushed into poverty if we had to live on one income - I have the option of gearing up again. And ploughing away loads into my pension, upgrading our property and saving for my dcs when they are 18. Financial security allows me to sleep at night.
Also, children need the parents around throughout their lives, not necessarily more when they are below 5. I keep hearing from more experienced mothers than their dcs need them more than ever at school age and teenagers. Hence, choose the option that is sustainable in the long term, not just one which allows you to stay with dcs when they are young but leaves a big question mark when they are past 5 as to whether you can get a decent job.