Hello,You need to live in the UK with the children for at least 3 years first (work, study etc.) and you may leave the UK for up to 90 days a year (i.e. up to 270 days over the 3 year period) without having any problems.
See here for further details:
http://www.ukba.homeoffice.gov.uk/britishcitizenship/eligibility/children/britishcitizen/livingintheuk/Hope this helps