Yes a mother can continue to breastfeed her kid while she is pregnent with a second child. The body of a mother continues to produce milk while she is pregnant. It is perfectly normal to brestfeed the toddler as the unborn baby will still get all the essential nutrients required. But yes it has to be taken care that the mother is taking a good care of her & having sufficient intake of essential nutrients so that there is no health issue for her & the unborn child.