Is it not necessary for someone whose urine has stopped and whose state of ritual impurity (hadath) is prolonged to perform istinja' (ritual cleansing), and is it sufficient to perform the first istinja' then wudu' and prayer, according to the Maliki school of thought?

The Maliki school of thought concerning a child's urine, in this scenario, is that it is excused and does not necessitate purification (istibra’) if it is a recurring impurity (comes once or more a day). In such a case, it is excused on the body and clothes. Ablution (wudu’) is obligatory unless it reaches the level of incontinence (sals). Entering the mosque with it is permissible as long as there is no fear of soiling it. The questioner's attribution to the Malikis is correct, but the view of the majority of scholars is more preponderant.