For these are no ordinary baby baths, but special 'Tummy Tubs', which are designed to make tiny tots feel snug and secure.
'Babies like to be confined - they are used to it,' explains a spokesman for the company. They instinctively go into a foetal position and they feel so at home. It's particularly good if they're colicky.'
Snug fit: Babies in Ijmuiden in The Netherlands try out the buckets, after a baby massage session
And what's more, because of the smaller surface area, the water in a Tummy Tub (which should initially be at body temperature) stays warm for much longer, so infants can stay in the tub for up to 15 minutes (as long as their shoulders are covered in water). And no, you couldn't get away with just dunking your child into the mop bucket.
The £20 tubs, which are available from Mothercare and John Lewis, have a rounded shape that makes them more comfortable, and there's also an anti-skid rubber ring on the bottom to stop them from flying across the floor.
So much for the tubs, then. But what about baby massage?
It may sound like a bit of a New-Age fad, but it actually has a long history of being used to calm fractious tots in Asian cultures.
'Basically, baby massage involves a mixture of lightly pressured stroking movements across the body,' says Michelle Powell, a certified infant massage instructor, based in Kingston, South-West London.
'As the movements relax the muscles and the baby is stroked in the same direction that a baby would make its bowel movements, massage can help relieve constipation and colic.
'The baby massage course usually lasts about four weeks, and every week we spend the 90-minute lesson concentrating on a different part of the body. So we might start with the legs and feet before moving to the stomach and chest.'
No wonder these babies - who all come from IJmuiden in the Netherlands - look so relaxed...
To find a baby massage class in your area contact the International Association of Infant Massage on 020 8989 9597 (prices usually start from about £10 a session).