Once babies get to between 4 and 7 months old, many parents are opting to buy a baby bath seat which will allow them to sit up whilst in the bath. This is because baby tubs tend too get a bit too small at this age but a regular bath is too big.
Some people say that bath rings and seats aren't a good idea because parents will be tempted to leave the baby to go and do other things. Make sure that if you buy a baby bath seat or baby ring that you always stay there with your baby.