Grindelwald
The most practical beginner base in the region, with the nursery area at the village edge.
Grindelwald wins because the learning happens beside the village, not a train ride above it. The Bodmi nursery area is gentle, sunny and well organized, the ski schools are large and used to English speaking families, and the modern gondolas make the step up to the Kleine Scheidegg blues painless.
It edges out Wengen because access is simpler, the village has the most shops, pools and rainy day options, and you skip the extra rail leg with tired children. It is also the only one of the three you can reach by car.