Kids' Swimwear Buying Guide: Fit, Fabric and Sun Safety

Quick answer

Buy swimwear that fits snugly at the shoulders, chest and leg openings, then size up only when a child is between sizes or still in swim diapers. Look for a fabric blend with stretch recovery, a UPF rating you can verify on the label, and a cut that covers the shoulders if your child burns easily. If you cannot find a UPF number, treat the garment as ordinary clothing and add sunscreen and shade.

Start with fit, not the size on the tag

Swimwear stretches when wet, so a suit that feels perfect on dry land can sag in the pool. Put it on, then have your child raise both arms and touch their toes. The straps should stay on the shoulders, the crotch should not pull down, and the leg openings should sit flat against the skin without digging in.

For toddlers, check that the leg openings are snug enough to hold a swim diaper in place. A loose leg opening lets water and solids escape, which defeats the purpose of a swim diaper. If the suit gaps at the leg but fits everywhere else, that cut is wrong for your child, not the size.

• Shoulder straps: should not slide off when arms are raised.
• Chest: should lie flat with no gaping when your child bends forward.
• Leg openings: should sit flat and hold a swim diaper securely.
• Torso: should not pull the shoulders down or ride up at the back.

Fabric: what stretch, chlorine and salt do to a swimsuit

Most kids' swimwear uses a blend of polyester or nylon with elastane for stretch. Elastane is what gives the suit its snap-back, and it is also the first thing to break down from chlorine, heat and sunscreen oils. A suit with a higher elastane percentage feels softer but tends to lose shape faster; a lower percentage holds up longer but feels firmer.

If your child swims several times a week in a chlorinated pool, choose a suit with a tighter, denser knit and rinse it in cool water immediately after every swim. If swimwear is mostly for holidays and garden play, a softer, lighter knit is more comfortable and easier to pull on and off.

UPF swimwear for kids: what the label actually tells you

UPF ratings describe how much UV radiation passes through the fabric, not how long a child can stay in the sun. A UPF 50 fabric blocks most UV, but it does not cover the face, hands, feet or any area the garment does not cover. Stretched fabric, wet fabric and worn fabric all provide less protection than the label suggests.

Use UPF swimwear as one layer of protection, not the whole plan. Pair it with shade, a hat, sunglasses where your child tolerates them, and sunscreen on exposed skin. If a garment has no UPF rating, do not assume it has one.

One-piece, two-piece or playsuit: match the cut to the child

One-pieces stay in place during jumping and diving but are harder to change out of when wet. Two-pieces are easier for toilet breaks and for children who dress themselves, but the top can ride up during active play. A playsuit style covers the torso and upper legs in one piece, which reduces the areas you need to reapply sunscreen and stays put during crawling and climbing.

For babies and young toddlers, a one-piece or playsuit is usually the most practical because it holds a swim diaper and does not separate in the water. For older children who manage their own bathroom breaks, a two-piece can reduce frustration and keep them independent.

Decision rules for buying kids' swimwear

• If your child is in swim diapers: Choose a one-piece or playsuit with snug leg openings. Check that the leg opening holds the diaper against the skin when your child squats. Loose legs mean leaks. Size down or change cut.
• If your child swims more than twice a week: Prioritize a denser knit with a moderate elastane percentage and rinse in cool water after every session. Expect to replace it sooner than a holiday-only suit. Chlorine is the main cause of stretched-out swimwear.
• If your child burns easily or swims at midday: Choose a cut that covers the shoulders and upper back, and verify a UPF rating on the label. Add a hat and sunscreen on the face, hands and feet. UPF fabric covers only what it touches.
• If your child dresses themselves: A two-piece is easier for toilet breaks, but check that the top does not ride up during play. A tankini-style top with a snug hem works better than a loose one. Independence matters, but so does coverage.

Bobo Choses pieces that fit this guide

• SB126AB086 Flying Oranges playsuit: The Flying Oranges playsuit is a one-piece style available in sizes 9 months and 12 months, part of the SS26 collection. A one-piece playsuit is the most practical cut for babies and young toddlers because it stays in place and helps hold a swim diaper.
• sb126ad079 Spicy window bambula crep dress: The Spicy window bambula crep dress is made in a lightweight crep fabric and comes in sizes S and M. A lightweight crep dress is a cover-up option for the walk to the pool or beach, not a substitute for swimwear or UPF protection in the water.
• Happy Worm long socks: Happy Worm long socks are made in Spain from 74% organic cotton, 24% polyamide and 2% elastane, in sizes 20-22 up to 38-40. Cotton socks are not swimwear, but the size range shows how Bobo Choses scales accessories by age, which helps you judge fit when ordering online.

Who this approach is for

Best for

• Parents buying a first swimsuit for a baby or toddler who is still in swim diapers
• Families who swim regularly in chlorinated pools and need swimwear that holds its shape
• Children who burn easily and need a cut with more shoulder and torso coverage

Not for

• Parents looking for a fashion-only cover-up; a lightweight dress or cotton socks are not swimwear
• Children who need a competitive or technical racing suit with a specific competition fit
• Anyone shopping for adult swimwear sizes or cuts