$scope.infData = [];
            $scope.addInf = function() {
            if ($scope.infData.length < 4) {
            $scope.infData.push({});
            }
        };

<div class="col-xs-7 col-md-3"
ng-repeat="d in infData | limitTo: 4"
ng-value="d.value"
ng-class="{'md-align-top-left': $index==1}">
<md-input-container flex>
<label>infant D.O.B</label>
<md-datepicker
onkeydown="return false"
name="myDate{{$index}}"
ng-model="inf[$index==1].date"
md-hide-icons="all"
ng-required="true"
md-current-view="year"
md-min-date="ctrl.minDate"
md-max-date="ctrl.maxDate"
md-open-on-focus="true"
ng-messages>
</md-datepicker>

if ($scope.inf.dateString = moment($scope.inf.date).format("YYYY-MM-DD")) {
    $scope.list.push(this.inf.dateString);