2.3.1. Child Development (IYCD)

The IYCD tool version 1.1 implemented in this study included 121 items: 46 motor (22 fine, 24 gross), 40 language (24 expressive, 16 receptive), and 35 socio-emotional items, which resulted from the feasibility study [14]. The tool was created for use on a tablet-based system using ODK (open data kit) with parent report items. The tool contains items such as: "Does your child reach for and hold objects at least for a few seconds?" (motor) or "Does your child use two words together in a meaningful phrase/speak in short two-word sentence? For example, 'mama go', 'give mama', 'daddy gone'." (language) or "Does your child ever try to imitate your actions around the house?" (socio-emotional). In each country, all items were translated by two local translators who knew the subject and then were back translated by two different language experts with consensus gained at each stage. Back translations in all countries were then checked by the subject matter expert team (M.G., P.K., M.J.) and were streamlined as much as possible between countries.

In the preliminary study, all children were assessed for all items despite their age, enabling us to determine the age at which 50% of children could achieve each item. For this main study, each item of the tool was then placed in order by the age at which approximately 50% of children could achieve it from these preliminary data. A starting point for asking each item was determined using the age of children first achieving the skills based on our previous meta-data synthesis and feasibility work [13,14]. In order to facilitate understanding of the items by caregivers, photos, videos or sounds were provided as appropriate (e.g., a sound example for "Does your child make single sounds like "buh" or "duh" or "muh"?). These were first selected and reviewed to consensus by the authors, then finalized based on feedback from the field teams, who also provided some of the

photos and videos. They were presented to the caregivers on tablets for each item that was highlighted in the tool as needing a prompt (Figure 2).

**Figure 2.** Example of items with prompts.
