Parents with children at a Sheung Shui kindergarten are calling for measures to be taken by a school bus company after a four-year-old girl using its cross-border service was left behind at Lo Wu on Monday. The school principal said it had no contract with the bus company but believed the increase in the number of students this year, boosted by the kindergarten education voucher system, could have played a part in the incident. A four-year-old girl, surnamed Ma, who travelled from her home in Shenzhen to attend classes on Choi Yuen Estate, was found by immigration officers who heard her cries and saw her alone at the Lo Wu checkpoint arrivals hall. The Sheung Shui Rhenish Church Kindergarten student was supposed to get off the bus, follow a woman supervisor, or 'bus mother', who had the girl's travel permits, then reboard the vehicle with other students after crossing the Lo Wu checkpoint. Officials informed the girl's outraged parents of the incident. Her father said the bus service was unreliable. Last week, he had to take his daughter to the first day of school when the bus failed to arrive on time. School principal Lilian Or Ngan-fung said the girl was accompanied by both parents when she travelled to and from the school yesterday. 'She seemed to be in good spirits and was willing to go into the classroom for her lessons,' Ms Or said. 'Some parents did call up and ask the school to help them distribute letters. They plan to hold a meeting next week to see how to improve the situation.' Ms Or said the school had no links with the bus company. 'We just help the bus companies distribute their cards, and parents are free to choose. 'But the company tells us that this year there is a new 'bus mother' and there are more students [crossing the border to attend school here] due to the introduction of the education voucher system.' Two cross-border bus companies serve the school, and Ms Or said some parents may have no choice if a company did not serve a particular route or area. The bus company was reported to have noticed the girl missing on the Hong Kong side just before she was due to have reached the immigration counter. An official public announcement was made regarding the girl and her parents were informed.