I would send e-mail so it in writing.

"There seem be a few instances of misunderstandings which I like to address before it escalates. I feel very important for open communication so I trust this taken in spirit intended.

1. Late pickup
Although I understand sometime if unavailable, it important that accurate information is sent. When told you were running late and would be here in 5 mins, I took face value, as you were aware my child had appointment. It very disappointing when that turn into 35 mins and it impacted on my personal time and family commitment considerably. This cannot happen again.

2. Drop off time
When care was arranged, you had requirement for 8am drop off time but you child typically coming much later. Since you only client with early drop off, please let me know (preferably night before) if not going to be here on time as that allow me to plan my own morning."

Do you have late collection fee? If not, add one. Mine $1 minute so for person who 35 min late, it $35 fee. Good deterrent.