Purchase tickets for the London Eye in advance and consider splurging on a fast track ticket. Have water and snacks handy for long waits. The Southbank area is very congested. There are long lines for rides and restaurants, especially during the summer.
The ticket office for the London Eye is about a block away from the attraction. Lines may be overwhelmingly long, both at the ticket office and the London Eye entrance. Fast track tickets will save you time from waiting in the queue but cost more.
Visit the London Eye as early as possible. Our first day attempting the London Eye was late in the afternoon. We did not purchase tickets in advance and the wait was 2 hours. We were told by an employee to come early the next morning for tickets. We had no problems the next day around 9 a.m. to purchase tickets at the ticket office.
Try riding the red double-decker buses. They are inexpensive, very easy to catch and the kids love them. The Tate Modern is free admission except for special exhibits. Children under the age of 12 have free admission for the special exhibits. Advance tickets purchased for the London Eye are cheaper than at the ticket office but you may risk waiting in the rain to get on the ride.