In short: what to fix and what to keep changeable
A child's room that changes with the child is done like this: the renovation fixes only what will be hard to alter later, meaning socket and light positions, lighting, built-in storage carcasses, flooring, sound insulation and blocking for anchoring furniture. Furniture, wall colour, textiles and decor stay changeable and cheap to replace.
The plan is drawn from the outset for three ages: toddler, school-age child and teenager. If all three fit the same electrics and storage, you will not need another renovation in five years.
Three stages worth drawing now
Toddler: plenty of clear floor for play, a changing chest, low open storage for toys, the cot away from the window and radiator. School age: a desk by the window with good light, shelves for books, somewhere for construction sets that cannot be packed away every night. Teenager: a 120 to 140 cm bed instead of a child's bed, a desk with a monitor, more closed storage and more privacy.
Draw all three plans over the same room. You see at once where the desk goes at each age, where the bigger bed will stand and which wall stays free. That is the basis for the electrics.
Electrics and lighting for the years ahead
Put sockets where they will be needed at every stage: by the bed on both possible sides, several in the future desk area along with a data point, and by the free wall for a TV or console. Use shuttered safety sockets, an ordinary product rather than a special system.
Lighting comes in three layers. General ceiling light on a dimmer, a directed light over the desk and a soft night light by the bed or at floor level. A switch by the door and another by the bed, at a height a school-age child can reach. Adding a light point later means chasing into the wall, and the three-age drawing shows where it will be needed.
Storage that grows with the child
The built-in wardrobe is made as a carcass for years to come, with an adjustable interior. The hanging rail first sits at a height a toddler can reach, then higher; shelves go on adjustable strips rather than fixed supports. Low open cubbies for toy boxes become bookshelves a few years later and then get doors.
Do not order themed or "age-specific" furniture for the built-in part: in three years it will all have to go. Keep the room's personality in what can be changed over a weekend: textiles, prints, the colour of one wall.
Floor, walls and noise
A child's room floor should feel warm underfoot, stand up to toy cars and chair legs and be easy to clean. Parquet with a hard-wearing finish or good-quality vinyl works better than fitted carpet, which is hard to clean. A rug goes on top, separate and replaceable.
Walls get washable paint. One wall can be given over to whatever changes: colour, wallpaper, a cork or magnetic board. If the room adjoins the parents' bedroom or the living room, think about sound insulation in that partition during the renovation: a toddler naps in the day, a teenager plays music in the evening, and in both cases a thin wall disturbs everyone.
Safety: no home-made solutions
Tall wardrobes and shelving are anchored to the wall according to the manufacturer's instructions. For the fixing to hold in a plasterboard partition, blocking is built in at the right spot, so the furniture positions need to be known before the walls are closed. Windows get opening restrictors that suit your window system, not improvised stops.
Choose furniture, fixings and systems that come with instructions and certified specifications, and take advice from competent professionals. A nice visualisation does not prove that a bunk bed or ladder is suitable for a particular child. That is checked against the product's documentation.
Two children: one shared room or two rooms
A large room for two children can be designed so it can be split with a partition later. That means two sets of electrical and lighting points, symmetrical storage and a plan for where the second door will go. Each resulting room must meet the requirements for habitable rooms: a window, floor area, ventilation. Check this with the architect before the renovation.
Adaptable does not mean buying today everything you will need in ten years. It means today's spending does not get in the way of tomorrow's changes. Keep a clear budget for the current stage and the services ready for all the ones that follow.