Hi Maureen,
You taking a huge step moving to the UK with a large family. What part are you planning on moving to? If London bear in mind, its extremely difficult to get accommodation due to the very high cost and social housing is virtually impossible to get due to benefit caps in place. Also bear in mind the welfare benefits are much lower in the UK than in Ireland. As far as I am aware it is only Jobseekers benefit that is transferable to another EU country for everything else you need to submit a new claim when you arrive in the UK. You will also need to apply for a National Insurance number, set up a bank account and register with the NHS.
http://jobsguideireland.com/transfer-jobseekers-benefit-abroad/ https:gov.uk/browse/benefits