Honestly we never really solved this problem, possibly though in part because our gaps were larger (4y4m and 3y8m respectively). Partly this meant the difference in needs was more extreme, partly the older child had slightly better skills at self entertaining/managing, partly 2nd & 3rd pregnancies were so bad that the preschool aged sibling was in preschool 4 days a week full hours by the end (because preschool was more fun than very sick mummy) and both times it seemed crazy to reduce preschool once the baby came as they were then so close to full time school. I realize that this post is useless, but i do feel your pain.
