Fila Giotto Turbo colour or Turbo Maxi felt tip pens.
Giotto range of produces is designed for younger artists. Using a water-based ink makes it washable at 40 degrees. The felt tip pens have ventilated lids and safety caps.

They also have an ultra-durable non-retracting tip.
With a good range of intense colours and made by one of the worlds biggest manufactures of art products, you cannot go wrong with these for your new little artists.