Basement experiments.

In London, as in other cities where children cannot on the whole be left to roam around unaccompanied, the great museums have traditionally provided opportunities for their exercise, amusement and instruction combined. Increasingly, museums have been reinventing themselves in efforts to become more popular - and thereby more profitable - in danger sometimes of overlaying the whole with a consumerist gloss.

One of the more inventive and modest of recent innovations is the basement addition of four new children's galleries to the Science Museum in South Kensington. The scheme, known as The Basement, was built by sponsorship and has the immediate advantage of not impinging on sensitive historic fabric. It makes lively sense of previously unusable subterranean space and accommodates about 2500 children a day.

In the interest of bringing children and science together in more practical ways, two galleries for the youngest age groups have been made experimental environments. Of the two, The Garden, designed by Casson Mann, for three to six year olds seemed the more successful because by simply being in it, the tots were involved. It is divided into 'construction', 'water', 'light and sound'. It has a satisfactorily squelchy path, squeaking noises, running water, things to climb on and handle, buttons to press. Things, for seven to eleven year olds, was devised by television's Eurotrash designer, Gilles Cenazandotti, famous for his surreal cardboard sets. It is brilliantly coloured and furnished with clever technological toys - computers, endoscopes - and visual tricks, but observation suggested that left to themselves, the children rather dashed from device to device without much concentration. The best contraption is a tilting shifting chair, inviting experiment and curiosity about the way chairs could be best put together. As in The Garden, the progression has been carefully worked out and there are helpers on hand.

The overall plan, by Ben Kelly, provides a new entrance for school groups on Imperial Road, a central constantly animated terrace which serves as a gathering point and antechamber to the galleries with numerous exits and entrances, and an informal theatre for lectures or performances. It is enthusiastically used as a picnic area from which to watch the lunchtime mime. As in the two galleries, children are encouraged to look at how things work - in this case, at the exposed innards of air-conditioning plant, of plumbing and lifts. Waste is a subtly conveyed theme, and littered around the place are silhouettes of familiar objects found discarded on the street. A cheerfully designed shop provides snacks and souvenirs, and child-scale lavatories have fittings lined up and carefully graded in size in Victorian manner.

Kelly was responsible for designing The Hacienda nightclub in Manchester, icon of early '80s youth culture and an early example of stripped down industrial chic. The Basement is reminiscent of this, for as in Manchester, Kelly has taken hold of the functional character of the place and elaborated on it with tough motifs like industrial chevrons, and acid colours - orange, lime green, pink - day-glo sharp against raw concrete and brick. A toplit arcade at the rear, providing access for wheelchairs and daylight, cleverly functions as an internal street, child-sized and marked by panels of these brilliant colours.