4. Xiao Pang, Xiao Dingding, Xiao Ya, and Xiao Qiao's four families, a total of 8 parents and 4 children, went to the amusement park together. The amusement park's ticket pricing is: 100 yuan per adult; 50 yuan per child; for 10 people or more, a group ticket is available at 70 yuan per person. They need to spend at least yuan to buy the tickets.
Answer: 800
Explanation: If parents all buy adult tickets and children all buy children's tickets, then it would cost: $100 \times 8 + 50 \times 4 = 1000$ (yuan); If everyone buys group tickets, then it would cost $70 \times (8 + 4) = 840$ (yuan), at this point, each adult pays 30 yuan less, and each child pays 20 yuan more. To spend the least amount of money, adults should buy group tickets as much as possible, and children should buy children's tickets as much as possible. Since group tickets require a minimum of 10 people, the best plan is: 10 people (8 adults + 2 children) buy group tickets, and the remaining 2 children buy children's tickets, which would cost $70 \times (8 + 2) + 50 \times 2 = 800$ (yuan).