Question:
Is there any easy/practical way
to temporarily (for several years) fill in a pool like this and then
later be able to return it to its original condition?
Answer:
Be sure the pool fence (it should have a safety fence) is also absolutely
secure, and beyond a child's capacity to climb (some children have amazing
climbing ability.
You might also consider a pool cover.
You are going to have to continue treating the pool water left in there so
that it doesn't breed mosquitos.
Give your children a water familiarization course ASAP, and continue doing
this as long as you are in the house. Do not rely on this to have the
children be able to get themselves out of the pool or swim, until they are
actually at an age to swim. My grandson, who has an inground pool (In FL)
was swimming pretty reliably at 3. But you can't rely on a 6 mo. old, no
matter what the people say. Incidentally try to have the water for these
classes warm enough, as cold children will resist and won't learn.