Look at non prickly/woody plants or fence the top? (as Children may fall into or down slopes when playing) Also consider is it sunny spot, shady, dry and do you want it low maintainance?
Best to choose plants with all year round interest (not too invasive) If your soil is Acid you could go for Ericas (Heathers), Pieris, Skimmia or Rhodoendrons (woody though).
If not look at the non invasive Hypericums, Cotoeaster horizontalis, Vincas (can be invasive) Pachysandra terminalis, Juniper horizontalis, Euonymous radicans. You could also after planting it, look at growing Clematis horizontally too.

I have a similar bank, planted with low-growing potentillas, geraniums (not pelargoniums), vinca, lonicera (worth its weight in gold) cotoneaster, wild strawberries, Ceratostigma plumbaginoides (I'm anxiously waiting to see if the latter survives the heavy frosts)

Plant Cotoneaster dammerii at the top and let it trail downwards. Any other rambling climbers would be good too such as Clematis. Also, anything that spreads by runners that root, like alpine strawberries or Polygonum affine which keeps its flowers (they are bronze later ) through winter.