Add value in name

try to concatenate like this: 1. Create a counter for the weekly array and an array for qtdcriancas; then the replay loop will access them

<select class="form-control" id="exampleFormControlSelect1" name="<?php $semanacrianca1[$a] ?>">

">

++ $ a; ++ $ b;

Now it goes from your logic to make funfar

Do this:

<?php  
 $i = 1;
 while ($i <= 2) {
?>
<div class="container">
 <div class="jumbotron">
  <h1>Dados da primeira Criança</h1> 
<form action="paginaAcao">

<div class="semanas-e-periodos">

<div class="form-group">
<label for="exampleFormControlSelect1">Semana</label>
<?php for($i=1;$i<=2;$i++){ ?>
  <select class="form-control" id="exampleFormControlSelect1" name="semanacrianca<?php echo $i?>">
   <option value="1semana">1º Semana</option>
   <option value="2semana">2º Semana</option>
   <option value="3semana">3º Semana</option>
   <option value="4semana">4º Semana</option>
  </select>
</div>
<?php } ?>
<div class="form-group">
<label for="exampleFormControlSelect1">Semana</label>
  <select class="form-control" id="exampleFormControlSelect1" name="qtdcriancas">
    <option value="1">1 Criança</option>
    <option value="2">2 Crianças</option>
    <option value="3">3 Crianças</option>
    <option value="4">4 Crianças</option>
    <option value="5">5 Crianças</option>
 </select>
</div>

</div>

</form>

</div>

<?php
 $i++;
 }
?>