A haven in a garden, a schoolyard, or a single planter
Most pollinator gardens fail not from a lack of flowers but from a gap in the calendar. Choose at least three plant species flowering in each of early spring, summer, and autumn so foraging bees are never left without food.
Widely recommended, well studied choices include crocus, willow catkins, and lungwort in early spring, lavender, borage, foxglove, and single flowered roses in summer, and sedum, aster, and ivy in autumn. Native wildflowers suited to your specific region generally outperform ornamental cultivars, since many showy double flowered varieties produce little nectar or pollen.
A single large pot of lavender or thyme on a balcony can support foraging bees for weeks. Herbs left to flower, such as basil, chives, oregano, and mint, are reliable, compact, and useful in the kitchen too.
Raised beds, a dedicated 'no mow' corner, and a simple insect hotel made from drilled wood or hollow stems give children a visible, safe way to observe pollinators. A small pond or water dish with pebbles for landing prevents bees from drowning while they drink.
Skip pesticide use on flowering plants, avoid double flowered ornamental varieties bred for looks over nectar, and resist the urge to tidy every hollow stem or bare patch of soil away in autumn, since these are exactly where many solitary bees spend the winter.