We are hoping to fly from the UK to Beijing with transfer in Amsterdam

The Netherlands to arrive at PEK at 06.15 on Thursday 12th July. Does the 144 hour period start at 00.01 on Friday 13th July so we would need to leave via PEK by 23.59 on Wednesday 18th July. The flight back is to Paris, France and we have a few days later in Paris and then we return to the UK. I assume children can get this transit visa as well? Are we able to get the 144 hour transit visa?

Thanks for any advice.