To sign for credits you have to fulfill the same conditions as Unemployment Benefit or Unemployment Assistance.
SIGNING FOR CREDITS
7. Under certain circumstances a person may be awarded credits without receiving a Benefit or Allowance payment. This may apply, for example, in the case of a person who has exhausted entitlement to Unemployment Benefit but who does not qualify for Unemployment Assistance due to their means. In this case, the person may be entitled to 'sign' for credits to protect their other social insurance entitlements. Signing for credits usually involves attending a Local DSFA Office at a specified number of times per year.
Credits may also be awarded to workers involved in an official trade dispute.
In order to be entitled to Unemployment Credits, a person must be available for full-time employment, capable of work and must also be genuinely seeking work. The additional requirement to be genuinely seeking work for the award of credits while unemployed is effective from 27 August 2003. This is taken from the welfare.ie website.
http://www.welfare.ie/foi/creditsaward.html#4
You mention that you may take the summer off to be with your children. If they are under 12 you can avail of the Homemakers Scheme. In a nutshell you will be awarded credits for the remainder of the tax year in which you start homemaking. Any complete year of homemaking will be disregarded when working out your yearly average for Old Age (Contributory) Pension.........soon to be replaced by State Pension (Contributory). When your youngest child reaches 12 or you resume work in the future you will also be awarded credits for that tax year.
It does seem very complex but it's quite easy when you read through the information available here.
http://www.welfare.ie/foi/homemaker.html and
http://www.welfare.ie/publications/sw1.pdf
Hope this helps and doesn't totally confuse you. If you need more clarication please PM me.