BMC Public Health 2008, 8:103 http://www.biomedcentral.com/1471-2458/8/103 Consequently, sample size calculations were undertaken for dietary outcomes using three day weighed food data on 18 month old Australian children [13,48]. As there are no quantitative dietary recommendations for children less than four years old in Australia, we suggest a 25% increase in vegetable consumption as a minimum target on which the sample size calculations are based. Australian data show that 18-month old children eat around 32 grams of vegetables (not including potato) per day with a standard deviation of 15 g [48]. To detect an increase in vegetable consumption as small as 25% the total number of subjects required is 112 (56 in each arm). To account for within-group clustering (resulting from randomisation at the first- time parent group level) the sample size was increased by the design effect/inflation factor of 2.8, based on assumptions of each cluster con- sisting of approximately ten people and a conservative inter-class cluster coefficient of 0.2. The sample size esti- mation was further adjusted to account for attrition (40%) with the potential of loss of entire groups to fol- low-up and we plan to over sample by 15%. Thus the final sample is 600 (300 in each arm). Randomization First-time parents groups will be randomised after recruit- ment in order to ensure baseline equivalence and mini- mise selection bias. Within each local government area, first-time parents groups will be randomly allocated to the intervention or control group in order of recruitment, using a computer generated random number schedule developed by a statistician who has no contact with the centres. Prior to the first intervention session families will be informed by letter regarding the outcome of randomi- sation. Table 1: Intervention time-frame and focus Infant Age Emerging Behaviours 3 mo 6 mo 9 mo 12 mo & 15 mo & 18 mo Early weaning and introduction of solids. Introduction of nutrient poor foods. Increased muscle control, strength and coordination. Adoption by parents of a feeding style and TV viewing habits Food rejection by infants Infant starts to: sit briefly unsupported; reaches with one hand; rolls over Increasing use of TV Parents' increased awareness of child mobility. Infant crawls and pulls self upright and walks with handhold Increasing autonomy of child in eating and activity Infant stands without support and beginning to walk Intervention group The intervention will be delivered by a dietitian and is comprised of six sessions delivered at three month inter- vals during the regular meeting time of the first-time par- ents' group (see Table 1). Based on an anticipatory guidance framework the intervention will incorporate a range of modes of delivery and educational strategies including brief didactic sessions, use of group discussion and peer support, exploration of perceived barriers, use of visual and written messages, follow-up delivery of mes- sages by text-messaging and mail-outs. All educational concepts will be developed iteratively, that is, messages will be repeated and expanded upon over the course of the intervention. Control group The control group families will receive usual care from their MCH nurse. In addition, these families will be sent general health newsletters (e.g. dental health, sun protec- tive behaviours, general safety), and will receive Birthday and Christmas cards. These families' participation will be rewarded with gifts (to a maximum value of $15.00) on receipt of completed questionnaires. Measures Parent and infant data will be collected using parent self- completion questionnaires, apart from infant dietary intake data which will be collected by telephone inter- view. As outlined in Table 2, all data (appropriate to the age of the child) will be collected every three months, cor- responding with the six intervention sessions. Repeated data collection is necessary given the rapid changes in height, weight, eating and activity behaviours in infants. The measures collected are detailed below. Anticipatory Guidance Intervention focus To introduce basic concepts regarding parental feeding styles and how these might relate to beliefs about parenting. To support parents to delay weaning/introduction of solids to 6 months To develop parents understanding regarding: *feeding styles and impact on children's eating *basic nutrition principals *sedentary behaviours in families and limits to acceptability To develop understanding regarding: * parental modeling of eating, sedentary and physical activity behaviours * impact of eating, activity and sedentary behaviours on health of children and adults and the provision of opportunities Continued development of themes/skills regarding: * eating and moving for health parents and children * how to feed/how to manage food rejection and demands * providing fail-safe food and activity environments Page 6 of 9 (page number not for citation purposes)